U.S. Nuclear Weapon Enduring Stockpile

Last changed 1 September 2001

Although the United States has produced something like 70,000 nuclear weapons of 71 major types since their invention, there are now roughly 9600 nuclear weapons of 10 major types (as determined by the official designation system) in the U.S. arsenal. The official name of this arsenal is the "Enduring Stockpile" and it is divided into three categories of warhead readiness.

Currently the U.S. is entering the latter part of an arsenal and readiness reduction process that began before the end of the Soviet Union during the administrations of Gorbachev and Bush. At the start of this process the United States had an active arsenal of some 23,000 weapons of 26 major types. Since that time actual nuclear warhead production has been completely shut down in the U.S. (although warhead modification, retrofit, and maintenance activities continue at a reduced level), most of the nuclear weapons manufacturing infrastructure has been dismantled, and the focus of the remaining nuclear infrastructure has shifted to dismantling surplus weapons.

This phase is coming to an end however, and under current plans will have halted by 2003. The dismantling activity is due to wind up in 1999 when the current backlog of retired weapons is disposed of. All of the weapons now in the U.S. stockpile are expected to remain in existence for the indefinite future, although nearly half will be transferred to lower levels of readiness. Barring further international agreements or diplomatic initiatives, this arsenal will remain basically unchanged.

The three levels of stockpile readiness are:

Active Service: Fully operational and mated with delivery systems
"Hedge" Stockpile: Fully operational (or can be made so on short notice) but kept in storage away from delivery systems, delivery systems are available for them however (this category currently has no weapons assigned to it)
Inactive Reserve: Weapon is kept basically intact, but is not maintained in operational condition (this principally means that tritium will not be stockpiled to charge the weapons tritium reservoirs), these weapons may not have ready-made delivery systems available

The reason that some 9600 weapons are currently slated for retention in some form or other, despite the signing of the START II treaty which reduces stockpiles to 3000-3500, is that

the START II treaty does not call for retired weapons to be dismantled; and
even though the U.S. Senate has ratified the treaty, the Russian Duma has not.

This means that the U.S. will not comply with START II until the treaty formally goes into effect, and because of the uncertain commitment of the Russian legislature to nuclear disarmament, the U.S. is keeping its options open by retaining hedge and inactive weapons.

At the Helsinki Summit on March 21, 1997, Presidents Bill Clinton and Boris Yeltsin announced a strategy to progress beyond this impasse. They proposed a START III treaty that would cut arsenals further - down to 2000-2500, and require the monitored destruction of at least some of the retired warheads. This is regarded as a more favorable situation for Russia than the one imposed by START II and may reduce political opposition.

The impact of the START III proposal on the U.S. arsenal is not clear, since the details have not been worked out, and U.S. stockpile policy has not been formulated. It may lead to at least the elimination of the inactive stockpile. The reductions in the active stockpile are likely to come largely from the numerous low yield W76 warheads, which may in turn lead to the early retirement of some Ohio-class ballistic missile submarines.

Currently all stockpile warheads are active service, except for a a small number of W84 cruise missile warheads which are inactive. Over the next several years nearly 5000 warheads will be transferred to hedge or inactive status. There are also about 2600 weapons awaiting dismantlement.

Actual production of new warheads halted in 1989. In January 1997, the first new weapon modification since the production shutdown entered service - the B61 Mod 11, a modification of B61 Mod 7s already in the stockpile. Starting in 1998 or 1999 a capability to remanufacture existing weapons at a low rate will be reestablished (but no new weapon production will occur).

The tables below give a summary breakdown of the U.S. enduring stockpile. Clicking on the last column of the table will bring up a detailed description of the correspondng weapon.

The Active Stockpile

Designation	Warhead Type	Yield (Kilotons)	Number	First Produced	Click For More Info
B53 Mod-1	Bomb-Strategic	9000	50	8/62
B61 Mod-3 Mod-4 Mod-7 Mod-10 Mod-11	Bomb Tactical Tactical Strategic Tactical Tactical/Strategic	0.3 / 1.5 / 60 / 170 0.3 / 1.5 / 10 / 45 10 / ? / 340 0.3 / 5 / 10 / 80 0.3? / ? / 340	600 (-3, -4, -10) 750 (-7, -11)	10/79 8/79 9/85 2/83 1/97
W62/Mk-12	Ballistic Missile Warhead/RV	170	610	3/70
W76/Mk-4	Ballistic Missile Warhead/RV	100	3000	6/78	No Graphic Available
W78/Mk-12a	Ballistic Missile Warhead/RV	335	920	8/79
W80 Mod 0 Mod 1 (ALCM) Mod 1 (ACM)	Cruise Missile Warhead Sea Launched Air Launched Air Launched	5 / 150	350 1000 400	12/83 12/81 ?/90
B83	Bomb-Strategic	low to 1200	650	6/83
W87/Mk-21	Ballistic Missile Warhead/RV	300 (upgradable to 475)	525	4/86
W88/Mk-5	Ballistic Missile Warhead/RV	475	400	9/88	No Graphic Available

The Inactive Stockpile

Designation	Warhead Type	Yield (Kilotons)	Number	First Produced	Click For More Info
W84	Cruise Missile Warhead	0.3 / ? / 150	350	6/83

Principal Sources:
Swords of Armageddon by Chuck Hansen, 1995
U.S. Nuclear Weapons: The Secret History by Chuck Hansen, 1988
Nuclear Weapons Databook: U.S. Nuclear Forces and Capabilities by Thomas B. Cochran, William M. Arkin, and Milton M. Hoenig, 1984
NRDC Nuclear Notebook prepared by Robert S. Norris and William Arkin of the Natural Resources Defense Council, published in The Bulletin of the Atomic Scientists.
Especially in issues:

July/August 1999
July/August 1998

Nuclear Weapons of the United States by James N. Gibson, 1996.