Cost-Effectiveness of Conventionally and Nuclear-Powered Aircraft Carriers
GAO/NSIAD-98-1 -- August 1998

OPERATIONAL EFFECTIVENESS OF CONVENTIONALLY AND NUCLEAR-POWERED CARRIERS ============================================================ Chapter 2 Our analysis indicates that conventionally powered and nuclear-powered carriers both have been effective in meeting national security objectives and requirements, share many characteristics and capabilities, and that the Navy employs them interchangeably. Our analysis shows that conventionally and nuclear-powered carriers both have been effective in fulfilling U.S. forward presence, crisis response, and war-fighting requirements. Both carrier types embark the same standard air wing and train to the same mission requirements. We also found that each carrier type possesses certain advantages. For example, conventionally powered carriers spend less time in extended maintenance and, as a result, can provide more forward presence coverage. By the same token, nuclear carriers can carry larger quantities of aviation fuel and munitions and, as a result, are less dependent upon at-sea replenishment. Both types of carriers in the Persian Gulf War effectively performed their war-fighting missions. We compared the two carrier types from the standpoints of their ability to fulfill U.S. forward presence, crisis response, and war-fighting requirements. Our comparison represents a historical perspective--the experiences of the Navy over the past several years operating a mixed force of conventionally powered and nuclear-powered ships.\1 That perspective addresses a broad spectrum of operations that includes providing routine peacetime presence, the Navy's response to emerging crises such as the movement of Iraqi forces to the Kuwait border in 1994, and the open conflict of Operation Desert Storm. -------------------- \1 With the exception of the first nuclear carrier, the U.S.S. Enterprise (CVN-65), the nuclear carriers operating with the fleet have all been 90,000 ton-plus Nimitz-class ships--the Navy's most recent carrier class. Conversely, the conventional carriers operating in the fleets have included ships of the World War II-era Midway-class, the first large-deck carriers of the Forrestal-class, the subsequent Kitty Hawk-class, and the U.S.S. Kennedy (CV-67)--a ship that was originally designed for nuclear propulsion. BOTH TYPES OF CARRIERS HAVE BEEN EFFECTIVE FULFILLING FORWARD PRESENCE REQUIREMENTS ---------------------------------------------------------- Chapter 2:1 Both conventionally and nuclear-powered carriers are employed overseas without consideration of propulsion type. Joint Staff and combatant command officials told us that the quality of presence provided by both types of carriers is indistinguishable. Conventionally powered carriers spend a smaller proportion of their time in depot-level maintenance than nuclear-powered carriers and, thus, are more available for deployment to meet presence and other fleet requirements. An all conventionally powered carrier force could either provide a greater level of overseas presence or require fewer carriers to meet U.S. peacetime presence requirements than would an all nuclear-powered force. BOTH CARRIER TYPES SATISFY THEATER COMMANDERS' NEEDS -------------------------------------------------------- Chapter 2:1.1 The Navy has employed a mixed force of conventional and nuclear carriers since the U.S.S. Enterprise's commissioning in 1962. During our discussions, officials of the Joint Chiefs of Staff, two unified commands, and the Navy could recall no instances since the Enterprise's commissioning where the United States failed to achieve its objectives because a conventionally powered carrier, rather than a nuclear-powered carrier, was employed. Officials from the Joint Staff and at two unified commands said that a carrier's type of propulsion is not a critical factor in making employment decisions. The unified command officials said that their concern is the mix and number of aircraft on board the carrier and that both types generate the same number of aircraft sorties--the critical purpose of the aircraft carrier. They also said that they had never specifically requested the scheduling and deployment of a nuclear-powered, rather than a conventionally powered, aircraft carrier. Overseas presence promotes regional stability by giving form and substance to the Nation's bilateral and multilateral security commitments and helps prevent the development of power vacuums and instability. It contributes to deterrence by demonstrating the Nation's determination to defend U.S., allied, and friendly interests in critical regions and better positions the United States to respond rapidly to crises. The presence posture enhances the effectiveness of coalition operations across the spectrum of conflict by promoting joint and combined training, encouraging responsibility sharing on the part of friends and allies, and facilitating regional integration. The Pacific Command uses a ¹Forward Presence Matrixº as part of its cooperative engagement strategy for the Pacific Region. The matrix outlines the Command's goals and states how it intends to achieve them, including port visits, exercises with foreign navies, Navy-to-Navy talks, personnel exchanges, and community relations projects. According to Command officials, the matrix makes no distinction between conventionally and nuclear-powered carriers--it is not an important issue--the only issue is having a carrier as a tangible indicator of U.S. presence. Unified command and Navy officials could not identify any instances where a presence mission or operation was adversely affected because a conventional rather than a nuclear carrier responded. However, many officials believed that a nuclear-powered carrier could respond more quickly over long distances and that because a commander is not concerned about the ship's fuel consumption, a nuclear-powered carrier can ¹just do it.º CONVENTIONALLY POWERED CARRIERS ARE MORE AVAILABLE DUE TO THEIR LESS DEMANDING MAINTENANCE REQUIREMENTS -------------------------------------------------------- Chapter 2:1.2 Because their maintenance requirements are not as stringent and complex as those of nuclear-powered aircraft carriers, conventional aircraft carriers spend a smaller proportion of their time in maintenance than do nuclear aircraft carriers and, thus, are more available for deployment and other fleet operations. During their service lives, aircraft carriers progress through a maintenance cycle of alternating operating intervals and depot-level maintenance periods.\2 In addition to the normal depot maintenance periods, nuclear-powered carriers must complete a refueling complex overhaul (RCOH) midway through their service lives.\3 While the conventional carriers do not have a similar requirement, during the 1980s and early 1990s, six underwent modernization, five of which had their service lives extended through the Service Life Extension Program (SLEP).\4 Given the large scope of its 1993 comprehensive overhaul and its expected service life, we included the U.S.S. John F. Kennedy (CV-67) among the six carriers.\5 We compared the proportion of time the two carrier types spent in depot-level maintenance from October 1984 through December 1996 and found that, collectively, the ships of each type spent about 30 percent of their time undergoing depot-level maintenance. However, during that time, three conventional carriers underwent a SLEP while, because of their relatively short times in service, none of the Nimitz-class nuclear carriers were refueled.\6 When we adjusted the data to reflect the time they would typically have spent in an overhaul, the conventional carriers would have collectively spent 24 percent of their time in depot-level maintenance--about 6 percent less time than did the nuclear carriers with complex overhauls. The difference between the two carrier types is generally consistent with their notional (planned) maintenance cycles. Figure 2.1 shows the notional (planned) maintenance cycle for conventional carriers extends over 72 months. The Nimitz-class nuclear carriers have been maintained within the parameters of an Engineered Operating Cycle (EOC), which, in its current form, extends over either 102 or 108 months, depending on the length of the overhaul at the end of the cycle. However, the Navy is changing the Nimitz-class maintenance cycle to an Incremental Maintenance Program (IMP), which will reduce the cycle time to 76.5 months. Figure 2.1: Comparison of Nuclear and Conventional Aircraft Carrier Maintenance Cycles Source: Navy data. Because less depot-level maintenance is needed, conventionally powered carriers would be available for fleet operations about 5 percent more than nuclear carriers during a single maintenance cycle. As table 2.1 shows, this is consistent with the adjusted data for the October 1984 through December 1996 period. Table 2.1 Notional Carrier Maintenance Cycles (Percent of time) Single maintenance cycle\a Over service life\b ---------------------- ---------------------- Available In depot Available In depot for maintenanc for maintenanc Type operations e operations e ---------------------- ---------- ---------- ---------- ---------- CV 75 25 74 26 CVN\c EOC 69 31 \d \d IMP 71 29 69 31 ---------------------------------------------------------------------- \a Based on one cycle, as shown in figure 2.1. \b Our analysis assumed a carrier's service life is to be 50 years for either conventional or nuclear power. The depot-level maintenance includes a SLEP for the conventional carriers and a RCOH for the nuclear carriers. \c All data is for Nimitz-class only and does not include U.S.S. Enterprise (CVN-65). \d Not calculated. Source: Our analysis of Navy data. -------------------- \2 Depot-level maintenance is normally performed in naval shipyards, private shipyards, or ship repair facilities. In addition to completing necessary repairs, modifications and alterations are made that improve the ships' capabilities. Because the procedures to maintain nuclear power plants are complex shipyard workers must be specifically trained to maintain nuclear carriers. Additionally, the materials used in nuclear carriers must meet exacting standards and the shipyards must have the facilities for the specialized work. \3 During a nuclear reactor's operation, the nuclear material in the core splits or is ¹burnedº as part of the fission process that produces the heat that generates the steam that powers the ship. Consequently, the core becomes progressively less efficient in generating the required heat and, therefore, at some point, must be replaced. Generally, a Nimitz-class carrier should be refueled after it has been in service for about 23 years, during the third complex overhaul (COH) or the fourth Docking Phased Incremental Availability (DPIA). Practically, the ship's operating tempo will also affect when it is refueled. In developing its maintenance schedules the Navy plans for a 32-month refueling period. \4 The objective of a SLEP was to restore and preserve the carrier's mission capabilities so that it could remain a first-line, battle group ship for up to 45 years of service. The modernizations averaged 32 months--ranging from 24 to 42 months. \5 The Kennedy now has a longer projected service life than the average of the carriers with a SLEP. \6 We did not include the Forrestal's SLEP in this adjustment since it did not occur entirely within our time period. CONVENTIONALLY POWERED CARRIER FORCE COULD PROVIDE MORE OVERSEAS PRESENCE THAN A LIKE-SIZED NUCLEAR FORCE -------------------------------------------------------- Chapter 2:1.3 An all conventionally powered carrier force could either provide a greater level of overseas presence or require fewer carriers to meet U.S. peacetime presence requirements than would an all nuclear-powered force. Providing the carriers needed to meet U.S. forward presence objectives in peacetime is an important determinant of the Navy's carrier force structure. In its 1993 Bottom-Up Review, DOD concluded a force of 10 aircraft carriers could meet the military's war-fighting requirements, but it retained 12 carriers (11 active carriers plus 1 deployable training carrier) to meet the larger peacetime forward presence requirements in the three principal overseas theaters.\7 (Those theaters include the Western Pacific, Indian Ocean, Persian Gulf, and Mediterranean Sea.) Currently, these carriers provide substantial, although not continuous presence.\8 The Global Naval Force Presence Policy sets priorities and provides scheduling guidance. -------------------- \7 DOD's report on the recently completed Quadrennial Defense Review stated that the Navy would maintain a force of 12 aircraft carrier battle groups. \8 DOD's Bottom-Up Review concluded that, with a 12-carrier force, the Navy could provide full-time coverage in one of the three regions while there would be a minimum of a 2-month gap in coverage during a year in each of the other two regions. According to the Global Naval Force Presence Policy, during gaps, a carrier battle group in another theater must be able to reach the "gapped" theater within a specified time frame. GLOBAL NAVAL FORCE PRESENCE POLICY ------------------------------------------------------ Chapter 2:1.3.1 During peacetime, the Chairman of the Joint Chiefs of Staff, service chiefs, and chiefs of the five unified geographic commands establish long-range planning guidance for the location and number of U.S. naval forces assigned to all regions on a fair-share basis.\9 This scheduling guidance--Global Naval Force Presence Policy--can be adjusted, as necessary, to meet unexpected contingencies. This policy results in planned gaps in various theaters, particularly in the Mediterranean Sea and the Indian Ocean. The policy represents a balanced distribution of naval assets while preserving personnel policy objectives. The policy does not differentiate between conventional and nuclear carriers. The naval forward presence requirements articulated by the Commanders in Chief of the European, Central, and Pacific Commands largely determine how the Navy deploys to meet its global commitments. The commanders base their requirements on the strategic objectives set for their theaters by the National Command Authorities\10 and the strategic situation in their theaters. According to a Navy doctrinal publication, "Overseas presence promotes national influence and access to critical global areas, builds regional coalitions and collective security, furthers stability, deters aggression, and provides initial crisis-response capability." The commanders believe that sustained, forward deployed, combat ready forces are vital to achieving these goals and are critical to ensuring timely crisis response. In its August 1994 assessment, Naval Forward Presence Report, DOD analyzed peacetime presence options for naval forces to meet the five geographic unified commands' unconstrained requirements for naval presence. It concluded that the unified commands' naval force requirements generally exceeded the levels of available assets. The report stated that "the totality of this set of all-encompassing requirements is beyond what could be reasonably covered by naval forces alone, it is a representation of the broad scope of presence missions confronting the theater commander" and that "any exercise in determining alternative force structures must necessarily account for other service contributions . . . ." The assessment also stated that the most important overseas presence requirements can be met through a range of measures, including "tethers,"\11 other service forces, and greater acceptance of periodic presence in some cases. Changing assumptions, such as operating tempo, availabilities, and originating ports and destinations, can also alter conclusions about force requirements. The Navy has periodically assessed naval force requirements using a model to calculate the total force necessary to meet the unified commands' presence requirements for given assumptions and inputs. The Navy deploys one carrier battle group and one amphibious ready group with an embarked, special operations-capable Marine expeditionary unit for a substantial portion of each year in the three theaters. According to the presence policy, if neither a carrier battle group nor an amphibious group is near an unfolding crisis, an equivalent force can be deployed to the vicinity on short notice from another theater. An important constraint that bounds the ability to employ carriers in support of forward presence is Personnel Tempo of Operations (PERSTEMPO). The Navy initiated the PERSTEMPO Program in 1985 to balance support of national objectives with reasonable operating conditions for naval personnel, coupling the professionalism associated with going to sea with a reasonable home life. The Program is built around the following goals: -- a maximum deployment length of 6 months, -- a minimum turn around ratio of 2.0:1 between deployments, and -- a minimum of 50 percent time in homeport for a unit over a 5-year cycle. The importance the Navy places on meeting PERSTEMPO goals is found in the presence policy that states that in scheduling carriers to meet these presence requirements, "CNO Perstempo goals remains inviolate." -------------------- \9 There are a total of nine unified combatant commands, five of which are called geographic unified commands, or theater commands. The five theater commands are the Atlantic, Central, European, Pacific, and Southern Commands. The commanders in chief of these commands are responsible for all operations within their designated geographic areas. \10 The President and the Secretary of Defense or their duly deputized alternates or successors constitute the National Command Authority. \11 Tether refers to the practice of maintaining ships at acceptable distances away from a specific area of presence operations while allowing them to return within a specified number of days. The tethered presence policy is a Chairman, Joint Chiefs of Staff, and DOD policy that is supported by funding in the fiscal year 1998 budget and the Future Years Defense Program for fiscal years 1998 through 2003. This policy results in lower force level requirements than those needed to support continuous presence in all three major regions. CALCULATING AIRCRAFT CARRIER OVERSEAS PRESENCE REQUIREMENTS ------------------------------------------------------ Chapter 2:1.3.2 Our analysis of force requirements estimates for overseas presence, derived from the Navy's Force Presence Model, shows an all conventional carrier force could either provide a greater level of overseas presence or require fewer carriers to meet U.S. peacetime presence requirements than would an all nuclear carrier force.\12 Several variables enter into the equation that calculates the carrier force level required to attain a level of peacetime presence. These variables include the time spent in depot-level maintenance, the restrictions imposed by the PERSTEMPO policy, the distance carriers must transit from their U.S. homeports to the overseas theater, the speed of the transit, and the length of deployment. Depot-level maintenance time is the single distinguishing variable when calculating conventionally and nuclear-powered carrier requirements. As table 2.2 shows, an all conventional carrier fleet generally could provide about 9 percent more presence coverage--an average of 32 days--in the European and Central Commands, while providing full-time coverage in the Western Pacific, than could an all nuclear fleet. Table 2.2 Presence Coverage Provided by Deployable Forces of 12-, 11-, and 10-Conventional and Nuclear Carriers Annual presence coverage\a -------------------------------------- All conventional force All nuclear force ------------------ ------------------ Deployable carriers\b Days Percent Days Percent ------------------------------ -------- -------- -------- -------- 12 369 101 336 92 11 336 92 303 83 10 303 83 274 75 ---------------------------------------------------------------------- \a Coverage provided to both the European and Central Commands over the course of a year. Includes a carrier homeported in Japan providing full-time presence in the Western Pacific. This example assumes that a nuclear-powered carrier can be permanently forward deployed in Japan. (Ch. 4 discusses the implications of this assumption in greater detail.) \b An additional carrier would be added to the above levels for each one that is in SLEP or RCOH or that serves as a dedicated training carrier. Source: Our analysis using the Force Presence Model. Table 2.3 shows the results of our analysis of the comparative number of carriers needed to provide various levels of overseas presence. Our estimates indicate that an all conventional carrier fleet generally needs about one less carrier to provide presence in the European and Central Commands and the Western Pacific than would an all nuclear fleet. Table 2.3 Number of Deployable Carriers Required to Provide 100, 80, and 60 Percent Presence Coverage 100 Percent\a 80 Percent\a 60 Percent\a -------------------- -------------------- -------------------- CVN CVN CVN -------------- -------------- -------------- CV EOC\b IMP\c CV EOC\b IMP\c CV EOC\b IMP\c -- -- ---- ------ ------ -- ---- ------ ------ -- ---- ------ ------ Nu 12 13 13 10 11 11 8 9 9 m b e r o f c a r r i e r s \ d -------------------------------------------------------------------------------- \a Percentage of time a carrier is present in European and Central Commands' areas of responsibility. Totals include the one carrier homeported in Japan, providing 100-percent presence coverage to the Western Pacific, regardless of propulsion type. (See ch. 4 for more information.) \b Nuclear carrier maintained under the EOC strategy. \c Nuclear carrier maintained under the IMP strategy. \d Rounded up to the next whole carrier. An additional carrier would be added to the above levels for each one that is in a SLEP or a RCOH or that serves as a dedicated training carrier. Source: Our analysis using the Force Presence Model. Neither the number of deployable carriers shown in table 2.2 nor the totals shown in table 2.3 provide for such needs as a training carrier or take into account extended maintenance periods such as nuclear carrier refuelings or conventional carrier service life extensions.\13 \14 Meeting those needs could require an additional one or two carriers. To minimize any factors other than propulsion type that could influence the number of carriers needed to provide forward presence, we based our calculations on the Navy's standard transit distances and the standard fixed transit speed of 14 knots.\15 The only delay we included in the transits was a 1-day delay for transiting the Suez Canal where appropriate.\16 The total requirement for the European and Central Commands is based on the assumption that Atlantic and Pacific Fleet ships would meet the presence requirements of those two Commands in the same proportion as they are currently scheduled for in the 1996 to 2000 time frame. We used the Navy's notional values, as inputs for operation cycle length (IMP cycle for nuclear carriers), deployment length, number of deployments per cycle, and overhaul length. -------------------- \12 The Navy uses this model to estimate the number of ships needed to provide overseas presence under specific conditions. \13 The Navy considers that it needs one carrier to meet the needs of the pilot training pipeline and to fill occasional gaps in its ability to meet peacetime presence requirements with the other carriers, as demonstrated by the Kennedy's recent deployment. \14 One conventional carrier was nearly continuously in SLEP while that program was underway. As the nuclear carrier fleet ages into the 21st Century, a similar situation will exist from a refueling overhaul standpoint. \15 Our calculations assume that the carriers are homeported in Norfolk, Virginia, and San Diego, California. \16 This delay occurred when an Atlantic Fleet carrier entered the Central Command's area of responsibility or when a Pacific Fleet carrier provided presence in the Mediterranean Sea. SEVERAL FACTORS AFFECT THE TIME NEEDED FOR THE CARRIER FORCE TO RESPOND TO A CRISIS OR MAJOR THEATER WAR ---------------------------------------------------------- Chapter 2:2 Several factors affect how quickly both types of carriers can respond to a crisis or mobilize for a major theater war. One factor is the speed the carrier and its accompanying battle group can maintain during their voyage to the crisis. Another factor is the degree to which any on-going depot-level maintenance periods and training periods can be shortened to accelerate deployment of the carrier. NUCLEAR-POWERED CARRIER'S UNLIMITED HIGH SPEED RANGE REDUCES TRANSIT TIMES -------------------------------------------------------- Chapter 2:2.1 Because nuclear-powered carriers do not need to slow for underway replenishment of propulsion fuel, they can transit long distances faster than can conventional carriers. Even though both types have similar top speeds, a conventional carrier normally slows to a speed of about 14 knots during underway replenishment. Our analysis showed that a conventional carrier, steaming at 28 knots, would arrive about 6 hours later than a nuclear carrier on a 12,000-nautical mile (nm) voyage (the distance from San Diego, California, to the Persian Gulf) and would have been refueled three times. On a 4,800-nautical mile voyage (the distance from Norfolk, Virginia, to the eastern Mediterranean Sea), the conventional carrier, steaming at 28 knots, would arrive about 2 hours later than a nuclear carrier. As table 2.4 shows, in most cases, a nuclear carrier completes a transit more quickly than does a conventional carrier. Table 2.4 compares carrier transit times only. Carriers being escorted by conventionally powered surface combatants would transit more slowly because of the escorts' need to replenish more frequently. As a result, the overall transit speeds of both types of carrier battle groups would be slower than those shown, if all of the ships in the battle group were to arrive in the same vicinity at about the same time. A comparison of transit times of nuclear and conventional carriers that have responded to several crises in this decade is presented in appendix IV. Table 2.4 Comparison of Nuclear and Conventional Carrier Transit Times Transit time (days) -------------- Transi t speed CV (knots refuelin Transit distance (nm) ) CVN CV\a gs\b ------------------------------------ ====== ------ ------ -------- 4,800 (Norfolk, Va., to th ---------------------------------------------------------------------- 20 10.0 10.0 0 24 8.3 8.4 1 28 7.1 7.2 1 8,600 (Norfolk, Va., to th Canal)\c ---------------------------------------------------------------------- 20 17.9 18.0 1 24 14.9 15.0 1 28 12.8 13.0 2 12,000 (San Diego, Calif., Gulf)\c ---------------------------------------------------------------------- 20 25.0 25.1 2 24 20.8 21.0 2 28 17.9 18.1 3 ---------------------------------------------------------------------- \a Transit time is based on the conventional carrier slowing to 14 knots for the duration of each refueling. \b The number of refuelings required is based on refueling the conventional carrier when its propulsion fuel level reaches 30 percent of capacity. \c This distance is to the central part of the Gulf. Source: Our analysis of Navy data. Figure 2.2 shows an oiler providing simultaneous replenishment with a Spruance-class destroyer and the nuclear-powered carrier U.S.S. George Washington (CVN-73) while transiting the Atlantic Ocean. Figure 2.2: An Oiler Providing Simultaneous Replenishment to a Surface Combatant and the Nuclear-Powered Carrier U.S.S. George Washington (CVN-73) Source: Navy photo. A CONVENTIONALLY POWERED CARRIER CAN MORE EASILY SURGE FROM MAINTENANCE -------------------------------------------------------- Chapter 2:2.2 If a carrier is required in an emergency, maintenance periods can be shortened by varying degrees, depending on the stage of the maintenance being performed. Navy officials said that it is easier to shorten the conventional carriers' maintenance periods than it is for those of the nuclear carriers and that this is an important factor governing the carriers' ability to respond to a major crisis. The degree to which a carrier undergoing depot-level maintenance can be ¹surgedº for deployment by shortening that maintenance period depends on how much of the period has been completed when the surge decision is made. For both types of carriers, the decision must be made early if the period is to be substantially shortened. However, Navy officials said, and documents show, that due to the complexity of its maintenance, a nuclear carrier's maintenance period cannot be shortened to the same degree as that of a conventional carrier. Also, a nuclear carrier's refueling overhaul cannot normally be shortened or accelerated since rushing the process would be neither economical nor prudent from a safety standpoint. Figure 2.3 illustrates the degree to which a conventional aircraft carrier can be surged out of an ongoing Selected Restricted Availability (SRA) and a nuclear aircraft carrier can be surged out of an ongoing Phased Incremental Availability (PIA) when the decision to do so is made at various times during the normal duration of those maintenance periods. The periods can be substantially shortened only if the decision is made early in the maintenance periods. Maintenance on both carrier types could be considerably curtailed if less than 15 percent of the scheduled maintenance time had been completed. However, a nuclear carrier's maintenance would normally proceed to its normal completion after about 33 percent of its scheduled maintenance had been completed, while a conventional carrier could complete up to 40 percent of its maintenance before proceeding to its normal completion. The figure also shows that a conventional carrier undergoing an SRA could be available to the fleet much quicker in an emergency than a nuclear carrier undergoing a PIA. Figure 2.3: Comparative Ability to Surge From an SRA and a PIA Source: Our analysis of Navy data. Figure 2.4 illustrates the difference in the ability between a conventional carrier undergoing a COH and a nuclear carrier undergoing a DPIA to surge from maintenance. Again, the decision to accelerate the maintenance period must be made early--before 15 percent is completed--if it is to be substantially shortened. Additionally, the periods will proceed to normal completion after about 33 and 40 percent of the nuclear and conventional carriers' maintenance periods, respectively, have been completed. Figure 2.4: Comparative Ability to Surge From a COH and a DPIA Source: Our analysis of Navy data. As the two figures show, while a conventional carrier can be more easily surged out of an SRA than a nuclear carrier can be surged out of a PIA, the reverse is true when a carrier is in either a COH or a DPIA. However, as figure 2.1 shows, SRAs and PIAs are the most common types of depot maintenance periods. Thus, from an overall depot-level maintenance standpoint, conventional carriers could more readily mobilize in response to a major crisis. BOTH TYPES OF CARRIERS TRAIN TO COMMON REQUIREMENTS -------------------------------------------------------- Chapter 2:2.3 The degree to which interdeployment training can be compressed is unrelated to a carrier's type of propulsion. Crews of nuclear and conventional carriers undergo the same interdeployment training except for training specifically related to the power plants. Two important factors in compressing interdeployment training are an air wing's proficiency and the turnover in the ship's crew since the last deployment. The Navy's Aircraft Carrier Training and Readiness Manual, which does not differentiate between nuclear and conventional carriers, describes the interdeployment training cycle. The cycle progresses through three phases of training--unit, ship and air wing, and battle group. The cycle also includes other activities such as in-port periods and preparation for deployment. Despite the common training program, our analysis of interdeployment cycle data since fiscal year 1984 shows that interdeployment training periods of conventional carriers have averaged 9.8 months while those of nuclear carriers have averaged 10.6 months. CONVENTIONALLY AND NUCLEAR-POWERED CARRIERS WERE BOTH EFFECTIVE IN THE PERSIAN GULF WAR ---------------------------------------------------------- Chapter 2:3 The Navy generally adhered to peacetime carrier deployment and maintenance schedules that had been established before Iraq invaded Kuwait and did not take any special actions to ensure a greater nuclear carrier presence during Operations Desert Shield and Desert Storm. Our review of data summarizing carrier operations and support during Desert Storm showed that both types of carrier were effective in their war-fighting missions. Details about the carriers' participation in Desert Storm are contained in appendix V. Given the presence of U.S. Air Force and allied aircraft, geographic constraints, and the relatively benign threat environment in the Persian Gulf and Red Sea carrier operating areas, Desert Storm may not be representative of the type of conflict in which nuclear carriers could demonstrate any of its operational advantages over conventional carriers. However, Desert Storm represents the most extensive and extended combat use of carrier aviation since the Vietnam conflict--before nuclear carriers comprised a significant portion of the U.S. carrier fleet. Additionally, it is the prototype of one of the two major theater wars or dangers that have been, and continue to be, a key element of U.S. military policy since the demise of the Soviet Union. Furthermore, Navy doctrine states the future role of naval forces has shifted from the Cold War-era independent blue-water, open-ocean naval operations on the flanks of the Soviet Union to a new emphasis on joint littoral operations in an expeditionary role against regional challenges. Thus, the nature of Desert Storm portends the types of conflict in which U.S. forces expect to be engaged in the foreseeable future. PRE-ESTABLISHED CARRIER SCHEDULES WERE FOLLOWED TO RESPOND TO DESERT SHIELD/DESERT STORM -------------------------------------------------------- Chapter 2:3.1 According to DOD's April 1992 report to the Congress entitled Conduct of the Persian Gulf War, during the first 2 months after the Iraqi invasion, the Commander in Chief, Central Command, believed there was a "window of vulnerability" when it was uncertain whether Coalition forces could defeat an Iraqi invasion of Saudi Arabia. As shown in figure 2.5, carriers generally deployed, returned from deployment, and began maintenance as scheduled during this period. Figure 2.5: Comparison of Previously Planned Carrier Deployments With Actual Desert Shield/Storm Deployments Note 1: Carriers' names highlighted in bold participated in Desert Shield/Desert Storm. Note 2: This schedule does not include either the Kitty Hawk (CV-63) which was undergoing Service Life Extension Program (SLEP) during the entire period, or Constellation (CV-64) which entered SLEP on July 1, 1990. Note 3: Planned deployment dates reflect the first day of the month when the deployment is to start, and the last day of the month when the deployment is to end. Source: Our analysis of Navy data. The Navy had several opportunities for a greater nuclear carrier presence in Desert Shield/Desert Storm but followed established deployment and maintenance schedules, as discussed below. -- The U.S.S. Eisenhower (CVN-69) was well into a scheduled 6-month deployment when Iraq invaded Kuwait. The Eisenhower entered the Red Sea on August 8th, remaining for 16 days, until relieved by the U.S.S. Saratoga (CV-60). Instead of being retained in theater during the initial period of uncertainty and concern following the invasion, the Eisenhower immediately departed for Norfolk and began shipyard maintenance in late October. Two conventionally powered carriers, the U.S.S. Kennedy (CV-67) and the Saratoga, were deployed for 7-1/2 months throughout all of Desert Shield/Desert Storm. -- The U.S.S. Carl Vinson (CVN-70) returned from a 6-month deployment on July 31, 1990, just 2 days before the Iraqi invasion. According to the Navy's tactical training manual, "Selected units [ships] returning from deployment can be retained for a period in a surge readiness status to meet contingency requirements." Instead, nonessential materials and supplies were offloaded during August and September, and the ship began a complex overhaul on September 29, 1990, lasting until April 1993. -- The U.S.S. America (CV-66) completed shipyard maintenance on August 2nd, the day of the Iraqi invasion, and underwent a significantly compressed 5-month training period, deploying for the war in December 1990. In contrast, the U.S.S. Nimitz (CVN-68), which had completed scheduled shipyard maintenance in April 1990, was used to qualify Reserve and student pilots in carrier landings for most of August and spent all of September and most of October in port in Bremerton, Washington. The ship did not deploy until February 25, 1991, 3 days before the end of the war. -- The U.S.S. Enterprise (CVN-65) arrived in Norfolk in March 1990, after completing a 6-month around-the-world deployment from Alameda, California. From the time of its arrival in Norfolk until the start of a RCOH in January 1991, the ship spent over 7 months in port, and about 1 month at sea conducting carrier landing qualifications and independent steaming activities. The Enterprise became nonoperational on August 15, 1990, less than 2 weeks after the Iraqi invasion, when the crew began removing everything not needed for the overhaul, which lasted over 3-1/2 years. Ultimately, the Navy deployed six carriers to fight in Desert Storm--the nuclear-powered U.S.S. Theodore Roosevelt (CVN-71) and five conventionally powered carriers: the World War II vintage U.S.S. Midway (CV-41), the U.S.S. Saratoga (CV-60), the U.S.S. Ranger (CV-61), the U.S.S. America (CV-66), and the U.S.S. John F. Kennedy (CV-67). LOGISTICS SUPPORT OF ALL CARRIERS WAS COMPARABLE -------------------------------------------------------- Chapter 2:3.2 The Navy operated and supported all six carriers in essentially the same manner. Each carrier battle group was assigned its own dedicated support ships, which enabled frequent replenishment of fuel and ordnance. All carriers were replenished about every 3 to 3-1/2 days, well before fuel and ordnance reached critical levels. Using Center for Naval Analyses-generated fuel and ordnance consumption rates, we estimate that the nuclear-powered U.S.S. Theodore Roosevelt (CVN-71) expended about 8 percent of its jet fuel and 2 percent of its ordnance per day, while the conventional carriers expended about 15 percent of their jet fuel and 5 percent of their ordnance per day. It is our observation that the carriers were resupplied whenever the opportunity arose, in accordance with naval doctrine, to maintain a high state of readiness. AIR OPERATIONS WERE COMPARABLE AMONG THE CARRIERS -------------------------------------------------------- Chapter 2:3.3 The distance to targets and the number of aircraft assigned to each carrier were primarily responsible for the differences in sorties launched by each carrier. Carriers operating in the Persian Gulf generated more missions than the Red Sea carriers because they were considerably closer to their targets. While the Roosevelt launched more sorties than any other carrier, it, along with the Kennedy, had the most aircraft assigned aboard (78). The Roosevelt operated in the Persian Gulf, while the Kennedy operated in the Red Sea. In contrast, two other Persian Gulf carriers, the Midway and the Ranger, had only 56 and 62 aircraft, respectively. When sorties were averaged based on the number of aircraft assigned, each of the Persian Gulf carriers averaged about 53 sorties per aircraft. None of the carriers operated around-the-clock. Instead, they rotated on an operating schedule that would enable them to have intervals of off-duty time for rest and replenishment. When sorties were analyzed based on operating days, the Roosevelt averaged 106 sorties per day compared to 89 for the Midway. However, the latter had 22 fewer aircraft aboard. When the number of assigned aircraft was considered, the Midway led all carriers with an average of 1.59 sorties per aircraft per operating day, followed by the Ranger with 1.41 sorties, and the Roosevelt with 1.36 sorties. CONVENTIONALLY AND NUCLEAR-POWERED CARRIERS SHARE MANY SIMILAR CHARACTERISTICS AND CAPABILITIES BUT DIFFER IN OTHERS ---------------------------------------------------------- Chapter 2:4 Even though the nuclear carriers are newer and larger than the conventional carriers, the two ship types have several common characteristics and capabilities. They are similar in that they -- are subject to the same operational guidance; -- carry the same number and types of aircraft in their air wing and can generate the same number of sorties; -- have top speeds in excess of 30 knots; -- do not differ with respect to their survivability; and -- can produce adequate supplies of fresh water. However, there are some differences. For example, nuclear carriers -- have larger storage areas for aviation fuel and ordnance and -- are better able to recover landing aircraft due to their superior acceleration. The similarities in these key features have allowed the Navy to employ both types of carriers interchangeably for routine deployments overseas and employment in contingency operations. OPERATIONAL GUIDANCE DOES NOT DISTINGUISH BETWEEN CARRIER TYPES -------------------------------------------------------- Chapter 2:4.1 When establishing the required capabilities of aircraft carriers, providing operational guidance, and preparing plans for employing them, the Joint Chiefs of Staff, unified commanders, and the Navy do not distinguish between conventional and nuclear carriers. Both carrier types are expected to carry out the same tasks, operate under similar conditions, and are allocated to peacetime presence missions and wartime tasks irrespective of propulsion type. For example, the document that discusses carrier missions and required operational capabilities states that the mission of multipurpose aircraft carriers is to operate offensively in a high density, multithreat environment. It lists specific tasks and readiness requirements but does not distinguish between the two carrier types. It also lists various readiness conditions under which the carriers must sustain operations. In meeting these conditions, there is no differentiation between conventional and nuclear carriers. Neither is there any differentiation in carrier types in setting requirements for overseas presence or in allocating assets to achieve presence objectives. The Joint Chiefs of Staff-approved Global Naval Force Presence Policy, for example, states the requirements for carrier presence in terms of the number of carriers allocated to each theater without specifying the type of carrier. Similarly, the guidance various headquarters and commands provide on transit speed, escorts, and fuel and ordnance loads does not differentiate between carrier types. The guidance we reviewed specifies the same maximum transit speeds for all carriers and requires that one or more surface combatants, such as a cruiser or a destroyer, are necessary at all times to escort and protect the aircraft carrier irrespective of propulsion type. The guidance also states that all ships will replenish their supplies after reaching a specified minimum level, which is the same for both conventional and nuclear carriers. The operational planning process for wartime does not distinguish between the two propulsion types. Joint Staff officials said that a carrier's type of propulsion is virtually transparent at their level. The Joint Staff apportions carriers to the unified commanders irrespective of propulsion type, and regional commanders prepare their operational plans based on the expectation that they will receive this specified number of carriers if the plans are executed. With the current mixed fleet of nuclear and conventional carriers, the specific carriers that will respond if the plans are executed will depend on the availability and readiness status of the individual carriers at that time. CONVENTIONALLY AND NUCLEAR-POWERED CARRIERS EMPLOY A STANDARD AIR WING -------------------------------------------------------- Chapter 2:4.2 The Navy's Policy for Carrier Battle Groups prescribes a standard composition for the air wings assigned to aircraft carriers. The standard composition is the same for both conventionally powered and nuclear-powered aircraft carriers.\17 The composition of an air wing is shown in table 2.5. Table 2.5 Composition of a Standard Carrier Air Wing Number of Aircraft Mission aircraft -------------- -------------------------------------------- -------- F-14 Strike/fighter 14 F/A-18 Strike/fighter 36 E-2C Airborne early warning 4 EA-6B Suppression of enemy air defense/electronic 4 warfare S-3B Antisubmarine warfare/anti-surface ship 8\a warfare/air refueling ES-3A Electronics intelligence 2 H-60 Antisubmarine warfare/search and rescue/ 6 utility ====================================================================== Total 74 ---------------------------------------------------------------------- \a The S-3 is normally used to refuel the wing's other aircraft during the launch/recovery process. However, it is not well-suited for refueling the other aircraft on long-range missions. On those missions, the air wing's aircraft frequently refuel from Air Force tanker aircraft such as the KC-135 and the KC-10. We examined the air wing composition of five carrier deployments (three conventional and two nuclear) and found that both carrier types deployed with only minor variations in the number of aircraft prescribed in the policy. Some deployments that included both carrier types carried one to three more support aircraft than the standard wing. With the embarked standard air wing, the two types of carriers are expected to generate the same number of sorties per day. During a crisis, a carrier may be tasked to fly more than the normal number of sorties or "surge" operations. The Battle Group Policy states that for augmented operations (during which an additional 12 strike-fighter aircraft would be assigned to the carrier), carriers must be able to generate 170 sorties per day during the initial crises response, 140 sorties per day for 3 to 5 days, and 90 sorties per day thereafter for sustained operations. Both types of carriers are subject to the same limitations of crew fatigue (both aircrew and ship's company) and equipment maintenance, which could affect sortie generation. For example, Navy regulations limit how much flight personnel can fly and mandate rest periods. Officials told us that deck crews and ordnance personnel would also be stressed during periods of increased sortie generation. Additionally, both types of carriers have the same catapult and arresting gear equipment that is subject to a strict inspection and maintenance schedule. These factors can limit a carrier's ability to generate sorties before aviation fuel and ordnance levels are depleted. As a result, the type of propulsion does not affect the length of time either carrier type could sustain periods of increased sortie generation. -------------------- \17 As noted in chapter 1, the aircraft carrier ¹maximum densityº is the same for both the U.S.S. John F. Kennedy (CV-67) and Nimitz-class (CVN-68) carriers. An aircraft carrier's capacity for carrying aircraft is expressed as aircraft carrier maximum density, a comparative number of F/A-18 equivalents that can be carried aboard a ship. Maximum density takes into account the space on the hanger and flight decks that the aircraft and helicopters in the air wing need as well as space for other items such as boats, boat skids, aircraft ground support equipment, forklifts, cranes, and aircraft jacks. It also allows for the clearances needed between the aircraft and between the aircraft and ship structures. The Navy's guidance on aircraft carrier density states that 75-78 percent of maximum density is the optimum number of aircraft to have aboard and that deck loading in excess of 80 percent must be coordinated with headquarters. Ship officials said that about 47-50 aircraft on the flight deck at any one time provides the flexibility to conduct flight operations and move aircraft on the flight deck and between the flight deck and hangar bay. TOP SPEEDS ARE SIMILAR -------------------------------------------------------- Chapter 2:4.3 The two types of carriers have similar top speeds--in excess of 30 knots. Additionally, neither type has any unique, propulsion-related constraints to maintaining speeds at that level for extended periods. One difference when sailing at high speeds is the conventional carrier's need to slow for underway refueling. However, as discussed earlier, the impact is minimal. According to Navy and shipyard officials, the method used to generate steam does not determine a carrier's top speed. Factors such as shaft horsepower, shaft torque limits, propeller design, displacement, and the naval architectural characteristics of the hull are the determinates of speed. Defense and Navy officials also said that other restraints preclude routinely sailing at high speeds for extended periods. Air crews have to fly periodically during a transit to remain qualified. Because a carrier would be unable to conduct flight operations during a 30-knot plus sustained voyage, the air crews would have to spend several days after arrival at the destination requalifying before they could be operationally employed.\18 Officials at one of the unified commands said that they would prefer to have a carrier battle group with trained crews arrive in their theater later than have one with an air wing that needed to requalify arrive earlier. High sea states and inclement weather could also preclude sustained, high speed voyages. A ship cannot sail fast in heavy weather without punishing the ship and its crew, regardless of its type of propulsion. Additionally, while the escorts in the battle group are generally capable of speeds in excess of 30 knots, they experience greater difficulty than carriers sustaining high speeds in very rough sea conditions. Also, as a Navy official pointed out, even at 30 knots, a long transit from the West Coast to the Central Command's area of responsibility would still take about 2 weeks. -------------------- \18 At high transit speeds, a carrier may not be able to maneuver as necessary to conduct flight operations. PROPULSION TYPE DOES NOT MATERIALLY AFFECT CARRIER SURVIVABILITY -------------------------------------------------------- Chapter 2:4.4 To successfully attack and degrade a U.S. aircraft carrier's ability to perform its mission, an enemy must detect the carrier and fix its location with sufficient accuracy so that one or more weapons can strike it. Additionally, the lethality of the attacking weapon(s) must be of sufficient magnitude to severely damage or sink the carrier. Officials of the Naval Sea Systems Command told us, according to their survivability analyses, neither type of carrier possesses any inherent, overriding advantage over the other in its susceptibility to detection or its vulnerability to the damage inflicted by the weapons.\19 They also said that the two types of carriers are very similar in construction, were built to the same shock standards, and use similar machinery and equipment. Thus, while there are some differences, neither has a distinct advantage withstanding or recovering from the effects of enemy weapons that can be attributed specifically to the ship's propulsion type.\20 Naval Sea Systems Command officials believe that the nuclear carrier's speed and unlimited range give it a distinct operational advantage, but they also told us that there were no analytical studies addressing these operational factors to support this belief. They said that these attributes allow a nuclear-powered carrier to employ tactics that minimize the risk of detection, thus reducing its overall susceptibility to attack. Additionally, a conventional carrier must be periodically refueled with propulsion fuel. Thus, it is susceptible to attack while alongside an oiler because it is steaming a steady course at a steady speed. A nuclear carrier is not as exposed to this susceptibility because it does not have to replenish its propulsion fuel. Both types of carriers, however, must periodically replenish their supply of aviation fuel. Since carriers normally replenish all supplies and fuel during an underway replenishment, a conventional carrier normally takes on ship propulsion fuel (DFM) and JP-5 simultaneously. However, the nuclear carrier still retains an advantage because, with its greater JP-5 capacity, it does not have to refuel as often.\21 Additionally, while refueling does restrict a carrier's ability to maneuver, the carrier typically moves to the rear to be less exposed when replenishing fuel, ammunition, and other supplies. That operation takes place under the defensive umbrella of the surface combatants of the battle group. -------------------- \19 DOD defines survivability as the capability of a system and crew to avoid or withstand a man-made hostile environment without suffering an abortive impairment of its ability to accomplish its designated mission. Susceptibility is the degree to which a weapon system is open to effective attack due to one or more inherent weakness (a function of operational tactics, countermeasures, probability of enemy fielding a threat, etc.). Vulnerability is the characteristic of a system that causes it to suffer a definite degradation as a result of having been subjected to a certain level of effects in an unnatural hostile environment. Both susceptibility and vulnerability are considered to be subsets of survivability. \20 The officials said that, while the more recent nuclear carriers have been built with enhanced magazine protection, this same level of protection could be incorporated in newly constructed conventional carriers. \21 During Operation Desert Storm, the conventionally powered carriers in the Persian Gulf replenished aviation fuel about every 2.7 to 3 days. The U.S.S. Roosevelt, the only nuclear-powered carrier in the Desert Storm air campaign also operating in the Persian Gulf, replenished its aviation fuel about every 3.3 days. FRESH WATER PRODUCTION CAPABILITIES ARE SIMILAR -------------------------------------------------------- Chapter 2:4.5 An adequate fresh water supply is critical to both types of ships. The steam that drives the turbines that propel the carriers through the water and powers the catapults that launch the aircraft is produced from fresh water. Fresh water is also used to cool equipment, for damage control, and to wash aircraft and the flight deck.\22 Both types of carriers need to retain fresh water reserves. About half of a nuclear carrier's fresh water storage capacity is for use as emergency reactor coolant. Finally, there is the requirement for ¹hotel services,º the water the crew uses daily for preparing meals, drinking, laundry, and personal hygiene. According to Newport News Shipbuilding officials, both types of carriers have essentially the same water requirements. Some of the older conventional carriers produce about 20,000 gallons a day less than the Nimitz-class, which can produce about 400,000 gallons per day. However, the U.S.S. Kennedy (CV-67) can produce 50,000 gallons a day more than the Nimitz-class. Navy officials said that any differences in fresh water production between conventional and nuclear carriers may be due to the conventional carriers' age. Newport News Shipbuilding officials also said that the differences are due to increases in the number of aircraft and personnel, not to differences in the propulsion type. Some Navy officials said that in harsh environments such as the Persian Gulf, conventional carriers frequently resort to water rationing to provide for essential services. Our review showed that the conventional carriers' ability to produce fresh water is similar to that of nuclear carriers and that rationing does not occur that frequently. Other Navy officials we met with discounted the problem of rationing aboard conventional carriers. They believe that fresh water shortages are, in many instances, indicative of management problems or inefficiencies aboard the ship--leaking boilers or pipes, for example. Some officials stated that, during their service, they had experienced water rationing as frequently, if not more frequently, aboard nuclear carriers as they had aboard conventional carriers. Officials, who had recently served aboard three conventional carriers in the Persian Gulf said that the ships had experienced no water rationing. -------------------- \22 Some Navy officials told us that conventional carriers use more fresh water to wash their aircraft to remove the boiler stack gas residue. NUCLEAR CARRIERS' DESIGN AFFORDS GREATER ORDNANCE AND AVIATION FUEL STORAGE CAPACITY -------------------------------------------------------- Chapter 2:4.6 The design of nuclear carriers has provided greater aviation fuel and ordnance storage capacity than conventional carriers, while their propulsion system has provided almost unlimited steaming endurance. Together, these factors could give nuclear carriers a decided operational advantage and superior war-fighting capability over their conventional counterparts if no at-sea logistics support were present. In reality, however, at-sea logistics support is present, and both carrier types and their surface escorts depend on this support to sustain operations. THE LARGER STORAGE CAPACITY OF NUCLEAR CARRIERS IS DUE PRIMARILY TO SHIP DESIGN ------------------------------------------------------ Chapter 2:4.6.1 The larger fuel and ordnance storage capacities of the nuclear carrier are primarily due to ship design differences that have little to do with the type of propulsion and the fact that nuclear carriers do not have to store large amounts of propulsion fuel. A ship's length, height, and width determine its internal volume, and as a result, the amount of fuel and ordnance that can be carried. Due to its larger hull size, the Nimitz-class nuclear aircraft carrier is about 10 percent larger than the last conventional carrier.\23 According to officials at Newport News Shipbuilding, the hull size of the nuclear carrier was more to provide increased space for ordnance, aviation fuel, and other supplies. The debate that took place when the Navy was originally considering building more nuclear aircraft carriers, in addition to the U.S.S. Enterprise (CVN-65), illustrates this point. For example, Admiral Rickover, in a 1964 letter to the Secretary of the Navy arguing that CV-67 be nuclear-powered, cited advantages of the Enterprise.\24 The letter states that the Enterprise hull is 50 feet longer than the CV-67's hull, which provides the 60-percent increase in ammunition storage. It also states the ". . . conventional carrier could also be built in an Enterprise size hull. This would provide an equivalent increase in the ammunition in the conventional carrier and would also provide a[n] . . . small increase (about 15%) in aviation fuel." Additionally, a 1992 Center for Naval Analyses research memorandum documenting the feasibility of five alternative aircraft carrier concepts developed by the Naval Sea Systems Command stated that, other than endurance range, a carrier built with a Nimitz-type hull but powered by a Kennedy-type oil-fired steam plant would be essentially equivalent to the Nimitz-class design. With enough propulsion fuel for a range of 8,000 nautical miles--a distance equal to about one-third the way around the world--at 20 knots (the equivalent of the current conventional carriers), the conventional variant would have the same magazine and aviation fuel (JP-5) capacities as today's CVN-68 class. -------------------- \23 The conventional carrier U.S.S. Kennedy (CV-67) has about 75 percent of the storage capacity of the first three nuclear ships of the Nimitz-class and about 80 percent of that of the U.S.S. Roosevelt (CVN-71) and the latter ships of the Nimitz-class. These latter ships have less storage space due to the addition of enhanced overhead and side protection that earlier Nimitz-class carriers lacked. \24 Admiral Rickover prepared the letter in his capacity as the Manager of Navy Reactors at the Atomic Energy Commission. AT-SEA REPLENISHMENT OFFSETS THE CONVENTIONAL CARRIER'S MORE LIMITED STORAGE CAPACITY AND ENDURANCE ------------------------------------------------------ Chapter 2:4.6.2 While nuclear carriers can operate for years before requiring propulsion fuel, they have a finite storage capacity for aviation fuel, ordnance, and other supplies. In addition, they are escorted by conventionally powered escorts, such as cruisers and destroyers, that require underway support due to their smaller fuel capacities and relatively high rate of fuel consumption. All surface combatant ships are highly dependent on regular resupply at sea. The Navy operates a Combat Logistics Force fleet of about 40 ships that resupply combatant ships at sea with ship and aircraft fuel, ordnance, food, and other supplies. The Combat Logistics Force enables combatant ships to operate at sea almost indefinitely, if required, without returning to port to replenish their stocks. The Combat Logistics Force consists of two basic types of ships--station ships and shuttle ships. Station ships, such as the AOE multipurpose fast combat support ship, are an integral element of carrier battle groups, routinely resupplying the other ships in the group. AOEs can simultaneously deliver fuel, ordnance, and other supplies.\25 The station ships provide the initial logistic support in theater until shuttle ships, such as fleet oilers and ammunition and other supply ships, can catch up. According to Navy logistics doctrine, station ships support a typical battle group with fuel for 20-30 days, consumables (other than fuel and ordnance) for 75 days, and spare parts for 90 days. The station ships, in turn, are generally replenished by ships that shuttle from forward naval bases to the battle group. At times, these single-product shuttle ships also replenish the combatant ships directly. The Combat Logistics Force represents additional days of sustainability for the naval force by serving as an extension of the combatant ships' bunkers, magazines and store rooms. See appendixes III and V for a more-detailed discussion of the impact of the Combat Logistics Force on carrier battle group operations. We compared the endurance of a notional conventional carrier battle group to a nuclear carrier battle group using Navy fuel and ordnance consumption rates contained in a 1993 Center for Naval Analyses report.\26 The notional battle groups we used consisted of either a conventional or nuclear carrier, plus two Ticonderoga-class Aegis guided missile cruisers (CG-47/52s), two Spruance-class destroyers (DD-963s), and two Arleigh Burke-class Aegis guided missile destroyers (DDG-51s). Each battle group was supported by one Sacramento-class supply ship (AOE-1). We estimated that the conventional battle group would have enough (1) fuel to steam for 29 days, (2) aviation fuel to operate at a tempo comparable to the final days of Desert Storm for 17 days, and (3) aircraft ordnance for 30 days. The conventional escorts of the nuclear carrier battle group would have enough fuel to steam for 34 days, while the nuclear carrier would have enough (1) aviation fuel to operate at a tempo comparable to the final days of Desert Storm for 23 days and (2) ordnance to operate for 41 days. -------------------- \25 The multipurpose fast combat supply ship (AOE) is the only noncombatant ship in the battle group and has the speed to keep up with the other ships. The Navy currently has four Sacramento-class (AOE-1) ships, and three slightly smaller Supply-class (AOE-6) ships, with one more being built. When an AOE is not available, a combination of ships can be used to carry out its role, such as oilers (AO) and ammunition ships (AE). However, these other types of ships do not carry the range of products that an AOE carries and, since their top speeds are about 20 knots, they do not have the speed to keep up with the other ships in the battle group. \26 Center for Naval Analyses Report 205, "Sizing the Combat Logistic Force," June 1993. The Center used 1990 and 1991 fleet data contained in the Navy Energy Usage Reporting System (NEURS) for fuel consumption and aircraft fuel and ordnance consumption based on the final days of Desert Storm. NUCLEAR CARRIERS HAVE A GREATER ACCELERATION CAPABILITY -------------------------------------------------------- Chapter 2:4.7 Navy officials said that a nuclear carrier would be better able to recover landing aircraft if wind and weather conditions suddenly changed or if the aircraft experienced mechanical difficulties, since it could accelerate more quickly than a conventional carrier to generate the additional ¹wind over deckº needed to safely land an aircraft.\27 The officials said that, under such conditions, a nuclear carrier can accelerate much quicker than a conventional carrier can because its reactors are always ¹on line.º According to Navy data, a nuclear carrier needs about 1-1/2 minutes to accelerate from 10 to 20 knots and about 3 minutes to accelerate from 10 to 30 knots. On the other hand, a conventional carrier steaming with four boilers on line producing steam can accelerate from 10 to 20 knots in about 2-1/2 minutes to 5 minutes. However, it cannot achieve 30 knots with four boilers--all eight boilers are needed.\28 If its eight boilers are on line, it needs as little as 12-1/2 minutes to accelerate from 10 to 30 knots. However, according to Navy officials, it can take as long as 1-1/2 to 2 hours to place boilers that are in a standby condition into full operation. According to fleet and ship officials, additional factors, such as preparing the flight deck, may affect the recovery of aircraft. They said that a ship's crew is aware of wind conditions during flight operations and, on a conventional carrier, they will normally have enough boilers on line so that the carrier can respond in a timely manner to recover landing aircraft. In addition, aerial tankers are always airborne during aircraft recovery to ensure that planes do not run low on fuel while waiting to land. Officials also noted that on a light wind day, both conventional and nuclear carriers may restrict flight operations rather than risk a situation where not enough wind over deck could be generated. Our review of Naval Safety Center data concerning carrier landings and Class A mishaps indicated that landing accidents of that magnitude are rare.\29 The Center identified 10 carrier-related landing mishaps from 1986 through 1996 (6 aboard conventional carriers and 4 aboard nuclear carriers). During that time period, there were about 545,000 and 470,000 landings aboard conventional and nuclear carriers, respectively. One Center official and fleet officials told us that the flight deck's layout plays a greater role in safety than does the ship's ability to accelerate. Such design features are not related to the ship's type of propulsion. Navy officials could not provide us examples of aircraft being lost because a conventional carrier could not accelerate fast enough. Additionally, a Naval Safety Center official told us that the Center had no record of an aircraft crashing because a carrier could not increase its speed quickly enough. -------------------- \27 The ¹wind over deckº is the sum of a carrier's speed and natural wind speed. Carrier aircraft have a minimum required ¹wind over deckº to safely land aboard a carrier. The ¹wind over deckº required varies by aircraft type and condition. A Navy official said that an F-14, for example, needs about 25 knots wind across the deck. There are some instances that would require natural wind in excess of 10 knots, even if the carrier was steaming at its top speed. \28 For example, the Kennedy's top speed, with four boilers on line, is about 26 knots. \29 DOD defines a Class A flight mishap as one involving a DOD aircraft with an intent to fly, which resulted in damages totaling $1 million or more, a destroyed aircraft, a fatality, or a permanent total disability. AGENCY COMMENTS AND OUR EVALUATION ---------------------------------------------------------- Chapter 2:5 DOD believed the draft report did not adequately address operational effectiveness features provided by nuclear power. According to DOD, any analysis of platform effectiveness should include mission, threat, and capabilities desired over the life of the ship. Further, it stated the draft report did not adequately address future requirements but relied on historical data and did not account for platform characteristics unrelated to propulsion type. That is, many of the differences may be explained by platform size, age, and onboard systems than by the type of propulsion. The Congress asked us to examine the cost-effectiveness of conventionally and nuclear-powered aircraft carrier propulsion. Such an analysis seeks to find the least costly alternative for achieving a given requirement. In this context, we used as the requirement DOD's national military strategy, which is intended to respond to threats against U.S. interests. That strategy encompasses overseas peacetime presence, crises response, and war-fighting capabilities. We used those objectives as the baseline of our analysis and selected several measures to compare the effectiveness of conventionally and nuclear-powered carriers. Those measures were discussed with numerous DOD, Joint Staff, and Navy officials at the outset. Those measures reflect the relative capabilities of each propulsion type, including the nuclear-powered carrier's greater aviation fuel and munitions capacity and unlimited range. Notwithstanding the enhanced capabilities of nuclear propulsion, we found that both types of carriers share many of the same characteristics and capabilities, that they are employed interchangeably, and that each carrier type possesses certain advantages. We also found that both types of carriers have demonstrated that each can meet the requirements of the national military strategy. We believe our methodology of reviewing a historical perspective covering a wide range of peacetime presence, crises response, and war-fighting scenarios that both types of carriers faced during the past 20 years is sound. A full discussion of our methodology can be found in appendix I. We continue to believe that this assessment will be helpful to the Navy as it assesses design concepts for a new class of aircraft carriers.