Overview Treaty Summary Treaty Text and Documents Archived Treaty Developments
Counting Rules
To return to the main Nuclear Disarmament Treaties and Agreements entry, see the Arms Control Treaties and Agreements file
For more recent developments, please see the General Nuclear Weapons Developments file.

Treaty Status

START I Treaty:
Signed: 31 July 1991
Ratified by the Russian Federation: 4 November 1992
Entered into force: 5 December 1994

Lisbon Protocol:
Signed: 23 May 1992

Treaty Summary

The START I treaty has a 15-year duration, with the option to extend it for additional five-year periods if all parties agree. During the 1997 Helsinki Summit, Presidents Clinton and Yeltsin agreed to negotiate an agreement that would make START I of indefinite duration. However, no such agreement has yet been negotiated.

The treaty limits the total number of strategic nuclear delivery vehicles for United States and Russia to 1,600 each, the total number of accountable warheads to 6,000 each, total number of warheads mounted on ballistic missiles (ICBMs and SLBMs) to 4,900 each, total number of warheads mounted on mobile ICBMs to 1,100 each, and the total ballistic missile throw-weight for each party to 3,600 metric tons (t). Additionally, START I permits Russia to have no more than 154 so-called "heavy" ICBMs (defined as having launch weight greater than 106t or a throw-weight greater than 4,350kg), specifically the R-36M-series [NATO designation SS-18 'Satan,' START designation RS-20] ICBMs, and no more than 1,540 warheads mounted on these missiles. The treaty also bans the construction of new types of heavy ICBMs and SLBMs, although it permits modernization programs and, in exceptional cases, new silo construction.

START I also bans the testing of missiles with a greater number of warheads than declared in the treaty, and bans any new ballistic missiles with more than 10 warheads. Parties to the treaty may also reduce the number of warheads attributed to a specific missile. However, no more than three existing missile types may have the number of warheads reduced, and the total reduction may not exceed 1,250 warheads. New missile types or heavy ICBMs may not be downloaded.

While the treaty counts each ICBM and SLBM reentry vehicle as a single warhead, counting rules for warheads attributed to heavy bombers are more complicated. Each Russian heavy bomber equipped to carry long-range nuclear ALCMs (defined as having maximum range of 600km or more), up to a total of 180 bombers, counts as eight warheads toward the 6,000 warhead limit, even though existing Russian heavy bomber types can carry between six and 16 ALCMs. Each Russian heavy bomber above the level of 180 has its actual number of ALCMs counted toward the 6,000 warhead limit. Similarly, each US long-range nuclear ALCM-carrying heavy bomber, up to a total of 150 bombers, counts as 10 warheads toward the 6,000 warhead limit, and each bomber in excess of 150 has the actual number of ALCMs it can carry counted toward the warhead limit. Bombers not equipped to carry long-range nuclear ALCMs are counted as one warhead.

START I contains extensive provisions for verification, including the use of National Technical Means, missile test telemetry tape exchanges, periodic data exchanges, monitoring activities, and on-site inspections.

Following the breakup of the Soviet Union, START I was modified by the Lisbon Protocol which  recognized the Russian Federation, Ukraine, Belarus, and Kazakhstan as parties to START I. The protocol also obligated Ukraine, Belarus, and Kazakhstan to accede to the Non-Proliferation Treaty as non-nuclear weapon states, leaving Russia as the only former Soviet republic owning nuclear weapons.

Treaty Documents

START I Treaty in English and Russian.  

Agreed Statements Annex

Definitions Annex

Protocol on the Joint Compliance and Inspection Commission

Notifications Protocol

Throw-weight Protocol

Conversion Protocol

Inspection Protocol

Inspection Protocol Annexes

Telemetry Protocol

Lisbon Protocol

[Entered 4/18/2001 MJ]

Page last updated 22 August 2001.
For more recent developments, see the General Nuclear Weapons Developments file.

This material is produced independently for NTI by the Center for Nonproliferation Studies at the Monterey Institute of International Studies and does not necessarily reflect the opinions of and has not been independently verified by NTI or its directors, officers, employees, agents. Copyright © 2002 by MIIS.

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