Scrapping the Unsafe Nuke

The author next to a B53 shape outside the Atomic Museum in Albuquerque, NM. This open-air display is located at these coordinates: 35° 3’54.78″N, 106°32’7.09″W.

By Hans M. Kristensen

The National Nuclear Surety Administration (NNSA) has announced that it has authorized the Pantex Plant in Texas to begin dismantlement of the B53 nuclear bomb.

Everything about the B53 is big: it weighs as much as a minivan and has an explosive yield of nine megatons, equivalent to 600 Hiroshima bombs.

Initially designed to annihilate Soviet cities, the large yield later earned the B53 one of the longest careers in the U.S. nuclear arsenal as a nuclear shovel; literally to dig up Soviet underground command bunkers. The mission was seen as so important that the B53 was even saved from an earlier retirement and allowed to serve for another decade until 1997 even though the Pentagon knew it had serious safety and security flaws.


The B53 is a two-stage thermonuclear bomb with a nuclear yield of nine megatons. At 148 inches (3.8 m) long and 50 inches (1.3 m) in diameter, the whole bomb weighs approximately 8,850 pounds (4 tons).

“Exploded” B53 Bomb Components
The behemoth B53 weighed as much as a minivan and had a yield of nine megatons. It’s mission was to destroy deeply buried facilities with enormous radioactive fallout as a consequence. Drawing obtained under the Freedom of Information Act.

Approximately 340 B53s of two versions (Mod 0 and Mod 1) were produced between 1962 and 1965. The bomb weighs as much as a minivan and could only be delivered by the B-52 bomber, each of which could carry two of the behemoth weapons.

The B53 only had a laydown option and was timer armed and fired so the delivery bomber had time to get away before detonation.

The large yield could destroy facilities buried 750 feet (230 meters) underground.


The B53 was on continuous airborne alert onboard B-52 bombers between 1962 and 1968, when about a dozen bombers were kept in the air 24 hours a day loaded with fully ready nuclear weapons to ensure the Soviet Union couldn’t disarm the United States in a first strike. After the airborne alert was canceled, the B53 was on ground-alert until retirement first began in 1987.

But that retirement coincided with the retirement of the high-yield Titan II ICBM in June 1987, another nine-megaton weapon used to hold Soviet underground facilities at risk. So the Joint Chiefs of Staff in March 1987 directed Strategic Air Command to return B53s to B-52 bombers on alert:

“In order to hold selected deeply targets at risk in all scenarios, a day-to-day alert capability is required. The current capability will be lost when the last Titan II ICBM is deactivated on Jun [sic] 87. Therefore, a B53 ALFA Alert capability must be developed as soon as possible.”

One of these targets probably was the nuclear command and control center under Kosvinsky Mountain in central Russia.

The B53 stayed on alert until 1991, when the bomber ground alert was finally cancelled.

Unsafe but Important

The B53 was not built with modern safety features, although it was one-point safe (detonation of any one chemical high explosives would not produce a nuclear yield). And over its many years in the stockpile some basic safety design features were added to the weapon to enhance nuclear explosive safety, for example to prevent accidental electrical energy from lightning to trigger the weapon. But the B53 did not have Enhanced Nuclear Detonation Safety (ENDS), Insensitive High Explosive (IHE), Fire-Resistant Pit (FRP), Protective Action Link (PAL), or Command Disable (CD).

The government had known about safety issues in the B53 “for twenty years,” former Sandia Director Paul Robinson later stated. But holding a few high-priority Soviet underground targets at risk was considered so important that safety requirements were waived, allowing the B53 to remain in the stockpile.

Legislation passed by Congress in 1992 specified three modern safety features that should be incorporated into all U.S. nuclear warheads: ENDS; IHE; FRP. The nuclear weapons stockpile plan from early 1993 directed the retirement of all warheads that lacked ENDS.

So in July 1993, then DOE Deputy Assistant Secretary for Military Application (Defense Programs) Winford Ellis “strongly recommended” to Harold Smith, the Assistant to the Secretary of Defense (Atomic Energy), that the B53 bomb be retired “at the earliest possible date.” The weapon “has no assured level of nuclear safety in a broad range of multiple abnormal environments.”

In addition to safety issues, the B-52 bomber was no longer considered capable of penetrating the most advanced air defense systems, so U.S. Strategic Command wanted a modern nuclear bunker-buster capability on the B-2 stealth bomber.

The B53 Replacement: The B61-11
The B-2 delivered B61-11 nuclear earth-penetrator (above, with spin motors in drop test) replaced the B-52 delivered B53 in 1997, improving the ability to penetrate modern air defenses and attack deeply buried facilities such as Russian command bunkers.

The September 1994 NPR recommended replacing the B53 with a new bunker-buster, which eventually became the B61-11, a modified version of the B61-7 with earth-penetrating capability and increased yield. As the B61-11 entered the stockpile in 1997 on the B-2 bomber, the B53 was finally retired for the second time.

Only one other warhead, the W62 on the Minuteman III ICBM, had worse surety features than the B53. The W62 was allowed to remain in service until 2009.

That Good Old Nuclear Secrecy

Now, don’t hold your breath to be told how many B53s are being dismantled. After the Obama administration in May declassified the entire history of the size of the nuclear weapons stockpile as well as the number of warheads dismantled each year, mysterious national security now requires the government to keep secret the number of B53s to be dismantled at Pantex. Some things never change.

Excessive secrecy aside, the number of B53s to be dismantled is approximately 36.

This publication was made possible by a grant from Carnegie Corporation of New York and Ploughshares Fund. The statements made and views expressed are solely the responsibility of the author.

2 thoughts on “Scrapping the Unsafe Nuke

  1. According to the Titan II book of David Stumpf the W53 of the Titan II is described as a warhead that was aimed against clusters of soft targets and not against hard ones because of the relative low CEP of the missile. Here you describe it as a “bunker buster”. What is correct?

  2. [Edited] Yield of weapon a relative term. In 1956 SAC order request on 120-megaton bomb (50,000-pounds), later this was reduced to 60mt and 25000 pounds (a new class A weapon). By early 1956 it was possible to fabricate TN weapons smaller than anything conceived two years earlier. AEC laboratories anticipated they could soon achieve a marked decrease in weight and marked increase in yield in four classes of TN weapons. For example, AEC predicted that new class A weapon would be built that would weigh not 50,000 pounds, as had its predecessor, but 25,000 pounds, and its yield wold be 60 Mt rather than the earlier 20 Mt.

    For those who had been starled by the destuctive power of the 20 kt bombs in 1945 and 1946, it must have been horrifying even to contemplate the possibility of a 60 Mt weapon. Yet in early 1957 AEC laboratories indicated that such a bomb might be devised in the not distant future. “In ca. 1957 LANL stated that 1000-megaton warhead could be built.” And in March 1958 the USAF Chief of Staff asked for a study of the feasibility of employing a weapons with a yields of 100 to 1000 MT. The Air Staff concluded that it might be feasible but not desirable to use a 1,000-megaton weapon. Since lethal radioactivity might not be contained within confines of an enemy state and since it might be impractical even to test such a weapon, the Air Force Council decided in April 1959 to postpone establishing a position on the issue”. Quotes from: The Air Force and Strategic Detterence 1951-1960. USAF historical devision LIASON OFFICE by George F. Lemmer 1967″. Formely restricted data.

    And I believe, however I [can] not find docs on it that very large cobalt-salted devices were studied in this timeframe. They might be a descendants (or versions) of gigaton mines. Gigaton mine concept was originated after Mike shot. These were multiple liquid deuterium stage devices, submarine size (14,000 tons) that were a single gigantic bomb. They would brought to coast of country and detonated. Such mine would contain (at least) 5000 tons of uranium. This would be a real hevy fallout. Global-killer bomb would require around 500,000 tons of cobalt and yielded several teratons.

    P.S. On yield of MK53. Mk53 was produced in two versions. In standart (dirty) Y1 – 340-350 were built, plus small number of Y2 (clean). Mk 53 warhead weight was 6,400 pounds, 8,500 pounds with FUFO. I don’t believe in 9 megatons, since I seen many docs that contradicts that; for example UCRL-ID-125506, A Pluto-Slam Design to Fit a Maximum Fineness Ratio Missile Into a Polaris Launch Tube. “Weapons: Optional configurations range from a single 32-inch diameter warhead, or pair of 21-inch diameter warheads, or as many as six 15-inch ejectable weapons. In each variant the total yield would be on the order of 10 megatons”. The weight of warheads was 4,000 pounds. I believe that all four classes have same yield-to-weight ratio -5.3 kt/kg. Since as 1.1 MT yield for Mk28 mod 0 Y1-yield of clean version, but this weapon never been produced in clean version (only produced ones in small numbers were Mk-36s Y2 (6 MT, down from 19 MT) and Mk-53 Y2), the predicted yield was a 800 kt, but this was only 20% of full yield, so yield was 4 MT (if yield was 1.1 MT thing never been carried by heavy bombers, only tactical bombers). MK53 Y1 must be 15 megatons in yield and Y2 5 megatons, so 9-10 MT is average value. Mk-53 intended have a yield of Mk-21 but in much smaller weight.

    Mk-21 yield was 14-15 megatons, 4-5 MT was yield of clean version (4.5 MT from Navaho test, but this was only at 1/3 of full yield). Sucessor of Mk-53 was a 35 MT warhead (~7,000 pounds), of Mk-41 55-60 MT (~11,000-12,000 pounds), both where designed by LLNL, but never produced (designs from 50 MT to 1,000 MT were apparently studied).

    20-megaton device tested in Poplar shot in clean version was considered as warhead for Navaho (predicted yield was 7 MT). This was a 9,000 pound, 2-stage device.

    Mk41 was considered as missile warhead at least twice – For USAF Pluto and Titan 2 A (A mean advanced). USAF plans were for at least 275 missiles. 4,000-pound (10 MT) warhead was considered as warhead for Advanced Minuteman.

    Reply: Whoa, a lot of data but hard to relate to given the absence of sources (other than USAF study). Are there some Chuck Hansen documents buried in there? HK

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