Growth and Evolution of the U.S. Nuclear Stockpile

The U.S. Nuclear Weapons Cost Study Project was completed in August 1998 and resulted in the book Atomic Audit: The Costs and Consequences of U.S. Nuclear Weapons Since 1940 edited by Stephen I. Schwartz. These project pages should be considered historical.

Sixty-five warhead types have been produced and deployed, configured for approximately 116 weapons systems. The air force has used 42 types of nuclear weapons, the navy and Marine Corps 34 types, and the army 21 types. Another 25 warhead types were canceled before production, because another warhead type was chosen, or in some cases, because the delivery system itself was canceled. Some warhead types have had wide applicability, used in one configuration as a bomb, and in another as a warhead for one or perhaps several kinds of missiles.


The last completely new warhead was a W88 assembled at the Pantex Plant on July 31, 1990 for the Trident II missile.


Although production has not resumed, Pantex recently converted approximately fifty existing B61-7 bombs into B61-11 bombs, to allow them to penetrate 10 to 20 feet (3 to 6 meters) into the earth's surface and destroy hardened underground targets. The principal modification is the emplacement of the existing "physics package" into a new needle-nosed, hardened, depleted uranium casing. This has increased the bomb's weight by 449 pounds (204 kilograms) and its length by just over 3 inches (8 centimeters). In addition, the drogue parachute has been removed, to permit the bomb to fall freely upon release and thus achieve maximum velocity prior to impact. While this program does not appear to contravene U.S. government pledges to foreswear development and deployment of entirely new nuclear weapons, it has raised serious questions about when a modified bomb becomes a new weapon. The B61-11 was first deployed with the B-2A bomber at Whiteman AFB in Missouri in April 1997. Scientists at Sandia National Laboratories are already designing a new nuclear glide bomb (based on the B61-11 but utilizing a new guidance system) to be dropped from the B-2A bomber, even though the Air Force has no requirement for such a weapon.


Other warhead modifications are underway: the W76 warhead for the Trident I missile is being revalidated (to ensure its continued conformity with military requirements in the absence of nuclear testing) and the pit for the W88 is being rebuilt (to address safety concerns pertaining to accidental detonation and plutonium scattering accidents first raised in 1990). In addition, the Navy and the weapons laboratories are engaged in a joint SLBM warhead protection program, the goal of which is to design and fabricate (but not actually produce) a new warhead for either the current or the next generation of SLBMs by 2004.


The historic high for the stockpile was reached in 1966 when about 32,200 nuclear warheads were simultaneously active. As can be seen in

figure 1-4

, the U.S. buildup started in the late 1950s and consisted almost entirely of tactical nuclear weapons, made possible by the rapid AEC production expansions in the early 1950s and the Eisenhower administration's "New Look" military program, which emphasized nuclear weapons over conventional forces. Annual production rates of nuclear weapons exceeded 7,000 a year in 1959-1960, and more than 5,000 in 1961: this amounted to almost 19,500 new warheads in three years, or a rate of about 25 per workday.

In 1954 hydrogen bombs — hundreds of times more powerful than their fission predecessors — began to enter the stockpile in great numbers, and the megatonnage increased sixty-fold in five years. It peaked in 1960 largely because the Strategic Air Command dominated the nuclear force of the day with a fleet of some 1,600 bombers, armed with thousands of high yield bombs (the explosive power of the arsenal today equals some 120,000-130,000 Hiroshima-sized bombs)..

With the sudden retirement of about 940 warheads in 1961, the megatonnage was cut almost in half. The reason was that the retired bomb, the B36, had a yield of 10 megatons. Until recently, the largest warhead in the arsenal was the 9-megaton B53 bomb, though only about fifty remained and were replaced following the introduction of the B61-11 into the active stockpile in April 1997.


As ballistic missiles were introduced and accuracy improved, high yield weapons were further reduced. The rule of thumb is that making a weapon twice as accurate allows an eight-fold reduction in yield to achieve the same level of destruction. Lower yields also permitted the use of substantially less plutonium and highly-enriched uranium in warheads, lowering the cost of many weapons and contributing to the eventual surplus of fissile materials.

— Robert S. Norris and Stephen I. Schwartz



For more information, see David Alan Rosenberg, "U.S. Nuclear Stockpile, 1945 to 1950,"

Bulletin of the Atomic Scientists,

vol. 38 ( May 1982), pp. 25-30; Robert S. Norris, Thomas B. Cochran, and William M. Arkin, "History of the Nuclear Stockpile,"

Bulletin of the Atomic Scientists,

vol.47 (August 1985), pp. 106-109; William Arkin, "The Buildup That Wasn't,"

Bulletin of the Atomic Scientists,

vol. 45 (January/February) 1989, pp. 6-10.



Letter from Gloria E. Inlow, Deputy Director, Office of Intergovernmental and External Affairs, Albuquerque Operations Office, U.S. Department of Energy, to Stephen I. Schwartz, July 19, 1991; R. Jeffrey Smith, "U.S. to Halt H-Bomb Production,"

Washington Post,

January 25, 1992, p. A1.



Greg Mello,

"New Bomb, No Mission," Bulletin of the Atomic Scientists,

vol. 53 (May/June 1997), pp. 28-32; Matthew L. Wald, "U.S. Refits a Nuclear Bomb To Destroy Enemy Bunkers,"

New York Times

(Washington edition), May 31, 1997, p. A1; William B. Scott, "Test Drops of B61-11 Penetrator Weapon Continue,"

Aviation Week & Space Technology,

June 9, 1997, pp. 75-76; Jonathan S. Landay, "US Quietly Adds A Bunker-Buster to Nuclear Arsenal,"

Christian Science Monitor,

April 8, 1997, p. 1; Jonathan Landay, "Why US Lab Is Designing Bomb No One Asked For,"

Christian Science Monitor,

July 24, 1997, p. 1; Jeff Erlich, "Bunker-Busting Bomb Prompts U.S. Discord,"

Defense News,

February 24-March 2, 1997, p. 1; William M. Arkin, "New, and Stupid,"

Bulletin of the Atomic Scientists,

vol. 52, no. 1 (1996), p. 64; Jonathan Weisman, "Old Nuclear Warheads Get New Life,"

Tri-Valley Herald

(Livermore, California), September 21, 1995, p. A1; John Fleck, "Sandia Redesigns N-Bomb,"

Albuquerque Journal,

September 22, 1995, p. A1; Jonathan Weisman, "Burrowing Nuclear Warhead Will Take Out The Atomic Trash,"

Oakland Tribune,

September 22, 1995, p. A1; Art Pine, "A-Bomb Against Libya Target Suggested,"

Los Angeles Times

(Washington Edition), April 24, 1996, p. A4.



Zerriffi, and Makhijani,

The Nuclear Safety Smokescreen,

p. 39; Elaine M. Grossman, "Navy, Energy Department Seek Back-Up Warhead Design for Trident Missiles,"

Inside the Pentagon,

May 9, 1996, p. 1; Elaine M. Grossman, "STRATCOM Has No Requirement for Alternative Trident Missile Warhead,"

Inside the Pentagon,

August 29, 1996, p. 6; John Fleck, "Labs Craft Warhead Backup,"

The Albuquerque Journal,

July 23, 1997, p. A1; U.S. Department of Energy,

FY 1998 Congressional Budget Request,

vol. 1, DOE/CR-0041 (GPO, 1997), pp. 57, 78; Office of the Secretary of Defense,

Nuclear Weapon Systems Sustainment Programs

(GPO, May 1997); Christopher E. Paine and Matthew G. McKinzie,

End Run: The U.S. Government's Plan for Designing Nuclear Weapons and Simulating Nuclear Explosions under the Comprehensive Test Ban Treaty,

Natural Resources Defense Council Nuclear Program (August 1997). The W76 recertification is necessary because when warhead production stopped in 1990, only about four hundred W88 warheads for the Trident II had been built. The W76 (which was not originally intended to be deployed on the Trident II) is thus being loaded on these missiles to offset the shortfall, and the program is to ensure that it will operate as designed.



Susanne M. Schafer, "B-2 Bombers Ready for Missions," Associated Press, March 31, 1997.


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