5"/54 MK 45 LWGM
Information Sheet Number: 1.1
The 5"/54 MK 45 Light Weight Gun Mount (LWGM) is the Navy's primary anti-surface gun battery, and Naval Gun Fire Support (NGFS) weapon. When a target is within the engagement envelope, the 5" gun is significantly more economical than a guided weapon. Versatile and extremely accurate, the gun is also used in an anti-air defense in depth capacity.
(a) SW323-DI-MMO-010/GM MK 45 MOD1
A. GENERAL INFORMATION
1. The MK 45 LWGM is the result of an extensive effort to produce a fully automatic intermediate caliber gun that would combine the following:
a. All weather capability
b. Low life cycle costs
c. Maximum safety to the ships crew
d. High mission availability
e. Minimum space and weight
2. Main battery for:
a. CGN 37, 41
b. DD 963
c. DDG 51, 993
d. LHA-1 (Tarawa)
e. CG 47
3. Provides defense against:
a. Surface craft
b. Low altitude aircraft (below 650)
c. Shore targets
B. CAPABILITIES AND LIMITATIONS
1. Rate of fire
a. 20 rounds per minute normal
b. 16 rounds per minute when using the fuse setter (ie. MT-PD)
2. Muzzle velocity
a. 2650 feet per second (FPS) full service charge
b. 1500 FPS reduced charge (defilade fire or illumination rounds)
a. 1700 either side of centerline
b. Mount movement is 300 per second
a. 800 total -15 to +65
b. Mount movement is 200 per second
C. PHYSICAL ATTRIBUTES
1. The MK 45 gun mount has two physical structure groups.
a. The lower structure (below deck) delivers an uninterrupted flow of ammunition.
b. Mount control (EP1, EP2)
c. Loader drum
d. Fuse setter
e. Lower hoist
f. Lower accumulator system
2. The upper structure loads the gun, lays the gun, fires and ejects the spent casing
d. Upper accumulator system
e. Gun laying system
g. Mount shield
3. Lower Accumulator System (LAS)
a. Located in the loader (ready service room)
(1) Used to maintain the hydraulic fluid pressure in the lower loading system between 1400 and 1550 PSI.
(2) Stores hydraulic fluid under pressure to meet peek demands that may exceed the output of the constant speed pump.
(3) Supplies fluid to the lower hoist, loader drum, ejector and fuse setter.
4. Upper Accumulator System (UAS)
a. Performs the same functions as the LAS.
b. Supplies fluid to upper gun loading system including: cradle, rammer, breech block, upper hoist and empty case ejector.
D. THE GUN LOADING SYSTEM
1. Lower hoist
a. Hoist drive
(1) Mounted next to the loader drum.
(2) Rotates an endless chain and lifts pawls (lifting mechanism) within the hoist and strikedown tubes.
b. Hoist loading station - located in the magazine, accepts powder cases and projectiles.
c. Strikedown loading/unloading stations
(1) Located in the ready service room and in the magazine.
(2) Only one powder or case at a time.
(3) Both station doors must be closed for operation.
d. Hoist tube - guides the ammunition between the hoist loading station and the loader drum in the ready service room.
e. Strikedown tube - guides the ammunition between the strikedown loading/unloading stations.
2. Loader drum
a. Located in the ready service room.
b. Receives and stores ammunition from the lower hoist.
c. Ejects rounds to the upper hoist
(1) Upper loading station - located at the top of the lower hoist and allows for the loading of special projectiles.
(2) Ammunition cells - twenty (20) cells are located within the drum cage for storage of projectiles and cases for expenditure.
(3) Transfer station - the transition point from drum into upper hoist.
(4) Fuse setter - located directly above transfer station; physically turns fuse cone to desired setting.
3. Upper Hoist
a. Receives rounds from the loader drum at the transfer station.
b. Raises rounds into the cradle.
c. Consists of a chain and pawl tube assembly.
a. Tubular structure centered above the upper hoist.
b. Pivots from the upper hoist to the slide.
c. Provides positioning for the rammer.
a. A chain driven pawl located in the cradle assembly.
b. Once the cradle has locked to the slide, the rammer begins its extend stroke, pushing the round into the breech.
6. Breech mechanism
a. Breech block seals to contain gases.
b. Lines up the firing point with the powder case primer.
c. Hydraulically operated, can be opened manually for maintenance with a special wrench.
7. Empty case extractors - hydraulic driven arms which pull spent cases from the breech into the empty case tray.
8. Empty case tray
a. Positioned directly behind breech during firing.
b. When the cradle raises to align a round with the breech, the empty case tray raises and aligns a spent case with an empty case tube and ejector.
9. Empty case ejector
a. Located above and to the right of the slide.
b. Case port is located above gun barrel.
c. A chain driven pawl, referred to as the ejector, pushes the spent case from the tray to the tube and out the port.
10. Gas ejection system
a. Two air ports located in the breech block guides
b. When the breech block opens, a cam triggers a burst of air through the gun barrel (175 PSI +/- 10 psi) expelling residual gases.
a. A rectangular structure attached to and pivoting on the trunions.
b. The slide is the mounting structure for the housing, empty case tray, the ejector and recoil systems.
a. The mounting block of the barrel
b. Contains the breech mechanism
c. Moves in the recoil/counter-recoil system
d. The housing is completely contained within the slide.
13. Recoil and counter-recoil systems
a. Recoil system
(1) Two pistons mounted in the cylinders in the gun housing and secured at the forward end of the gun slide
(2) By displacing hydraulic fluid through a system of orifices, the pistons slow the rearward motion of the housing
b. Counter-recoil system
(1) Two pistons located behind the gun housing in nitrogen charged flasks. One side of the differential piston is filled with oil while the other is exposed to the nitrogen charge.
(2) The recoil of the gun is opposed by the nitrogen pressure side which is transmitted to the oil side of the differential piston which returns the gun to battery.
a. A ring shaped structure bolted to a foundation on the ship's weather deck
b. Contains the roller bearings and training circle gear
c. Supports the rotating parts of the mount
a. The rotatable mounting base for all the above deck components of the gun mount
b. Rides the roller bearings and roller paths
c. Main components include:
(1) Base Ring - forms the contact surface with the stand and supports the rest of the carriage components.
(2) Trunnion supports - provide the support and pivot points for the gun slide and barrel.
(3) Carriage cable reel - mounted to the base ring; functions to keep flexible service lines taut when the carriage is rotating.
a. Aluminum house mounted to the base ring
b. Protects the mount from the elements
c. Two access doors, one per side
d. Pneumatic seals prevent water entry
E. LOADING OPERATIONS
1. For load and fire operations the gun mount requires the following orders:
a. Train and elevation
b. Breech loading
c. Single or continuous loading
d. Fuze setting
e. Firing order
2. Load/firing sequence
a. Ammunition handlers manually insert projectile/powder case at lower loading station
b. Lower hoist raises the projectile to load station ejector
c. Round transferred to loader drum and indexes to transfer station
d. Fuse setter sets fuse
e. Firing order
f. Ejector put round into upper hoist
g. Upper hoist raises round to the cradle
h. Cradle raises projectile
i. Rammer extends then retracts
j. Empty case ejector and cradle to slide latch retracts
k. Cradle lowers
l. Breech block closes
m. Empty case tray lowers
n. Gun fires
o. Gun recoils/counter-recoils
p. Breech opens and extractor removes spent case
q. Gas ejector expel gases
r. Empty case tray raises
s. Empty case ejector extends and expels case
F. GUN MOUNT CONTROL SYSTEMS
1. EP1 panel
a. Acts as an electrical switchboard
b. Located in the ready service room
c. Source of power for all systems
d. Converts ship's power to usable voltages
e. Components include:
(1) Circuit breakers
(2) Overload relays
(4) Power supplies (transformers)
(5) Indicating lights
2. EP2 Panel
a. Located in ready service room
b. Local control panel
c. Controls all functions of the gun loading system
d. Indicating lights allow operator to monitor all gun loading and laying functions
e. Components include:
(1) Motor start switches
(2) Gun system indicating lights
(3) Set up switches for modes of operation
(4) Step load push buttons
(5) Emergency firing switches
(6) Train and elevation local control dials
(7) Rear of panel contains logic status board
3. EP3 Panel
a. A digital display that reflects the type of ammo requested by the EP2 operator
4. Gun laying system
a. Sub-system of the gun mount which provides train and elevation motion.
b. Types of control orders
(1) Remote order signal from weapons control
(2) Local order from EP2 panel
c. Order source transmits a signal for train and elevation which represents desired positioning of the gun.
d. The difference between actual position and ordered represents the train and elevation error.
e. Control synchros in the receiver-regulator transforms the physical error into an electrical signal.
f. The servo control unit interprets the error signal and current gun motion then generates a correctional order to the hydraulic transmission.
g. The mechanical responses of the gun subtract from the error signal until synchronization of gun position and order is attained.
G. GUN MOUNT MANNING
1. All members of the gun crew are stationed below the main deck.
2. Not manned during Condition IV.
3. An optimum crew of three people is needed to operate the mount during Condition III (peace time steaming).
a. Mount Captain
b. EP2 Panel Operator
c. Special ammunition handler
d. 20 rounds loaded in drum
4. Condition I (General Quarters)
a. Mount Captain
b. EP2 Panel Operator
c. Petty Officer In Charge (POIC) of the magazine
d. 2 Powder loaders
e. 2 Projectile loaders
f. 4 Ammunition passers
5. During Condition III "Sustained Firing Operations" such as NGFS, a reduced GQ manning can be utilized.
a. Mount captain
b. EP2 panel operator
c. Special ammunition passer
d. 4 magazine crew
6. Duties of personnel
a. Mount Captain
(1) Supervises the training, performance, and adherence to regulations of all mount personnel.
(2) Supervises the maintenance of the mount and records.
(3) Receives and transmits activation, operation and deactivation orders as received from Weapons Control.
b. EP2 Panel Operator (may be Mount Captain)
(1) Positions switches that control gun mount operation (on order of Mount Captain).
(2) Monitors the indicating/warning lights of the EP2 panel during mount operations.
(3) Reports all problems to Mount Captain.
(4) Relays ammunition requirements to the POIC of the magazine crew.
c. Ammunition Handlers
(1) Special ammunition handler, located in the ready service room, load special purpose projectiles as called for by Weapons control.
(2) Petty Officer In Charge is an experienced Gunners Mate who supervises ammunition handlers.
(3) Ammo handlers are required to be qualified per the Qualification and Certification Program. They load the lower hoist as ordered by EP2 Operator.