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"[Arms Control Today is] Absolutely essential reading for the upcoming Congressional budget debate on the 2018 #NPR and its specific recommendations ... well-informed, insightful, balanced, and filled with common sense."

– Frank Klotz
former Administrator of the National Nuclear Security Administration
March 7, 2018
START I at a Glance
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Contacts: Daryl Kimball, Executive Director, (202) 463-8270 x107

Updated: February 2019

Strategic Arms Reduction Treaty (START) I was signed July 31, 1991, by the United States and the Soviet Union. Five months later, the Soviet Union dissolved, leaving four independent states in possession of strategic nuclear weapons: Russia, Belarus, Ukraine, and Kazakhstan. On May 23, 1992, the United States and the four nuclear-capable successor states to the Soviet Union signed the Lisbon Protocol, which made all five nations party to the START I agreement. START I entered into force Dec. 5, 1994, when the five treaty parties exchanged instruments of ratification in Budapest. All treaty parties met the agreement's Dec. 5, 2001 implementation deadline. START I expired on Dec. 5, 2009.

On 31 July 1991, the US President, George Bush (sitting on the left), and General Secretary of the Communist Party of the Soviet Union, Mikhail Gorbachev (sitting on the right), sign the START I Agreement for the mutual elimination of the two countries’ strategic nuclear weapons. (Photo: Susan Biddle/Bush Library)Basic Terms:

  • 1,600 deployed intercontinental ballistic missiles (ICBMs), submarine-launched ballistic missiles (SLBMs), and heavy (long-range) bombers for each side.
  • 6,000 "accountable" warheads on ICBMs, SLBMs, and heavy bombers, of which no more than 4,900 may be on ICBMs and SLBMs, 1,540 on heavy missiles (the Soviet SS-18), and 1,100 on mobile ICBMs (RSM-12M Topol).
  • Ballistic missile throw-weight (lifting power) is limited to 3,600 metric tons on each side.

Counting Rules:

  • Heavy bombers equipped only with bombs or short-range attack missiles (SRAMs) are counted as carrying one warhead each.
  • U.S. heavy bombers may carry no more than 20 long-range air-launched cruise missiles (ALCMs) each. The first 150 of these bombers count as carrying only 10 ALCMs each.
  • Soviet heavy bombers may carry no more than 16 ALCMs each. The first 180 of these bombers count as carrying only eight ALCMs each.
  • No more than 1,250 warheads may be "downloaded" (removed from) and not counted on existing multiple-warhead ballistic missiles.

Other Provisions:

  • START I ran for 15 years with an option to extend for successive five-year periods. Based on commitments made at the March 1997 Helsinki Summit, the sides agreed in principle to negotiate an agreement making the START treaties unlimited in duration.
  • Separate "politically binding" agreements limit each side to 880 sea-launched cruise missiles with ranges above 600 kilometers and the Soviet Backfire bomber to 500 kilometers.

For more Nuclear Arms Control Agreements between the U.S. and Russia, see: https://www.armscontrol.org/factsheets/USRussiaNuclearAgreements