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Treaty between the United States of America and the Union of Soviet Socialist Republics on Strategic Offensive Reductions (START I)

START I limited the number of strategic nuclear delivery vehicles and warheads. START II complemented START I by attempting to establish further limits on strategic nuclear weapons for each party.

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31 July 1991

Lisbon Protocol: Signed 23 May 1992

Entered into Force

5 December 1994


15 year duration with option to extend for unlimited five year periods, if all parties agree


5 December 2009

Treaty Overview

The U.S.-Soviet Strategic Arms Reduction Treaty, known as START I, was signed 31 July 1991 by U.S. President George H.W. Bush and Soviet President Mikhail Gorbachev.

START I was the first treaty to provide for deep reductions of U.S. and Soviet/Russian strategic nuclear weapons. It played an indispensable role in ensuring the predictability and stability of the strategic balance and serving as a framework for even deeper reductions. Even though many elements of START I — first and foremost the limits on the number of warheads and delivery vehicles — quickly became outdated, its verification and transparency provisions maintained their value until the treaty’s last days. At the same time, START I proved to be excessively complicated, cumbersome and expensive to continue, which eventually led the United States and Russia to replace it with a new treaty in 2010.

Negotiations that led to the signing of START I began in May 1982. In November 1983, the Soviet Union “discontinued” talks after the United States began deploying intermediate-range missiles in Europe. In January 1985, U.S. Secretary of State George Schultz and Soviet Foreign Minister Andrey Gromyko agreed on a new formula for three-part negotiations that encompassed strategic weapons, intermediate-range forces and missile defense. These talks received a significant boost at the Reykjavik summit between Presidents Ronald Reagan and Mikhail Gorbachev. In December 1987, the Intermediate-Range Nuclear Forces Treaty was signed. Negotiations subsequently turned to the reduction of strategic weapons.

START I entered into force on December 5, 1994. The break-up of the Soviet Union in December 1991 and the need to make arrangements with regard to its nuclear inheritance contributed to a three-year delay between the signing of the treaty and its entry into force. Principles for adapting START I to new political realities were agreed upon in May 1992 in the Lisbon Protocol. According to that agreement, four post-Soviet states — Russia, Belarus, Kazakhstan, and Ukraine — were recognized as parties to START I in place of the Soviet Union, but only Russia was designated a nuclear weapon state, while the other three assumed an obligation to join the NPT as non-nuclear states and eliminate all START I accountable weapons and associated facilities within seven years (the period of reductions mandated by the treaty). Whereas Belarus and Kazakhstan quickly joined the NPT and ratified START I “as is,” Ukraine experienced intense domestic debates over how to deal with its nuclear inheritance that dragged on for more than two years; its first START I ratification resolution was rejected by the United States and Russia.

Although the entry into force of START I took more than three years, some important activities were conducted shortly after its signing, most notably exchange of data on strategic weapons and associated facilities, as well as inspections to verify data on technical characteristics of strategic missiles and implementation of provisions on test launches and telemetry exchanges.

START I had a duration of 15 years. Reductions mandated by the treaty were to be completed no later than seven years after its entry into force. Parties were then obligated to maintain those limits during the next eight years. In fact, both the United States and Russia continued reductions after reaching START I mandated limits. By the time of the treaty’s expiration, their strategic nuclear arsenals were significantly below those stipulated in the treaty.

During the 1990s, the United States and Russia undertook several attempts to replace START I with a new treaty that would have provided for deeper reductions. The 1993 START II treaty never entered into force due to what Russia perceived as serious deficiencies of that treaty. Consultations on another treaty, sometimes referred to as START III, were conducted from 1997-2000 but ended without result. The Moscow Treaty provided for significantly lower limits on strategic weapons, but lacked verification and transparency provisions.

START I remained in force until December 5, 2009. It contained the option of extending the treaty for five-year periods, but Washington and Moscow decided against extension — negotiations were already underway on a new, replacement treaty, and START I was allowed to expire.



START I established an aggregate limit of 1,600 delivery vehicles and 6,000 warheads for each party (a reduction from 10-12,000 warheads in 1991). Within that limit, the Treaty established three sub-limits: 4,900 warheads for ICBMs (land-based intercontinental ballistic missiles) and SLBMs (submarine-launched ballistic missiles), 154 heavy ICBMs (defined as having a launch weight greater than 106t or a throw-weight greater than 4,350kg), 1,540 warheads for these heavy ICBMs (Only the Soviet Union possessed this type of missile), and 1,100 warheads for mobile ICBMs (de facto applied only to the Soviet Union and Russia because the United States, shortly after the signing of START I, decided to forego deployment of such missiles). The Treaty also established a limit of 3,600 metric tons (t) for the throw-weight of ballistic missiles.

The construction of new types of heavy ICBMs and SLBMs is banned, although modernization programs and, in exceptional cases, new silo construction, are permitted.

The treaty bans the testing of missiles equipped with a greater number of warheads than established 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.

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 U.S. 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.


Verification and Compliance

START I contains extensive provisions for verification. These include:

1. National Technical Means (NTMs), together with a ban on actions that impair the effectiveness of NTMs of the other party;

2. Data exchange: Accompanying the START I treaty is a Memorandum of Understanding drafted by the two parties, which contains an extensive set of data, including numbers and locations of all strategic delivery vehicles, both deployed and non-deployed, as well the locations and diagrams of all facilities associated with strategic delivery vehicles, such as bases, storage and production facilities, etc. Each party is required to provide notification about any change in that data shortly after it occurs. In addition, parties must exchange the entire set of data contained in the Memorandum every six months;

3. On-site inspections to verify the accuracy of data contained in the Memorandum of Understanding. Some of those inspections are short-notice (baseline data, data update, reentry vehicle, etc.) while others are “planned” (verification of technical data, the right to observe elimination of missiles and facilities, etc.). The treaty also provides for a special verification regime for mobile ICBMs. During the first seven years (the period of reductions), the United States conducted 335 inspections; Russia conducted 243.

4. Perimeter and portal monitoring of plants that produce mobile ICBMs. Because the United States decided not to deploy such missiles, this measure only applies to Russia: the United States established monitoring at the Votkinsk plant (or, rather, continued, because its monitoring began under the INF Treaty);

5. A ban on encryption of telemetry transmitted from ballistic missiles during test launches and exchange of all such telemetry.




Russian Foreign Minister Sergei Lavrov declared in front of the State Duma that if the United States further pursues the deployment of an anti-missile shield near Russian border, it might “force us to use the article of the treaty that provides for the withdrawal of a state that feels violated in terms of security.” Lavrov is referring to Article 14, which gives both countries a right to withdraw from the agreement.


On 8 April 2010 in Prague, U.S. President Barack Obama and Russian President Dimitri Medvedev signed the New START Treaty, and Protocol.


Negotiations on a new START Treaty began on 18 May in Moscow and continued throughout the year.

On 1 July, the last data exchange prior to START’s expiration took place in the START Aggregate Numbers of Strategic Offensive Arms. Data exchanges occur no later than 30 days after the expiration of each six-month period following entry into force of the Treaty.

START I expired on 5 December. Negotiations were put on hold during the American and Russian holidays.

As the treaty expired, U.S. inspectors ended their 15-year perimeter and portal continuous monitoring mission at the Votkinsk Machine Building Plant, which produces the SS-26 Bulava, the SS-27 Topol-M, and its new MIRVed variant, the RS-24. START I permitted continuous monitoring at ICBM production facilities in order to confirm the number of mobile launchers produced. Russia was unable to maintain reciprocal monitoring at an American production facility after the United States halted the production of Peacekeeper missiles in Promontory, Utah in April 2000.


On 7 April, after a bilateral meeting in Sochi, Russia, Putin stated that Russia would continue working with the United States to maintain all the useful and necessary parts of the START treaty.

On 9 April, the United States announced that the Nunn-Lugar Cooperative Threat Reduction program completed the elimination of SS-24 “scalpel” ICBM, including their supporting components, in accordance to START I obligations.

On 29 May, Russia announced that it had dismantled 36 outdated Topol mobile ballistic missile systems in 2007 and twelve in two consecutive operations in March and May 2008 under the provisions of the START I treaty.

On 11 September, Russian Foreign Minister Lavrov stated Russia was still awaiting concrete proposals from the United States, a statement confirming Russian sources contending that the U.S. had not supplied necessary working papers to move the negotiation process forward.

On 29 September, Russian Foreign Minister Lavrov stated that the bilateral negotiations on the future of START were “not so far heading anywhere.”


In March, the United States and Russia commenced bilateral consultations at the level of the deputy minister to explore a post-START agreement, including a possible extension of certain verification elements of the treaty.

In July, statements were made at an informal meeting between U.S. President George W. Bush and Russian President Vladimir Putin in Kennebunkport, Maine, expressing support for the replacement of START I, which expires at the end of 2009. While there were no direct talks pertaining to the START I treaty during the meeting, Secretary of State Condoleezza Rice and Russian Foreign Minister Sergei Lavrov commented that both countries were committed to reducing strategic arms levels to “the lowest possible level consistent with their national security requirements.” Supporters of the START treaty process expressed hope that the dialogue was to encourage a disarmament discussion in the future.


On 4 January, the Russian Defense Ministry accused the United States of violating its START I obligations of disarmament in regards to the U.S. LGM-118A Peacekeeper ICBM. The United States considered destroying the first stage of the Peacekeeper to be sufficient under START I guidelines. However, the Russian Defense Ministry contended that all stages of the missile must be destroyed under START I. In response, the Pentagon claimed that the second and third stages of the Peacekeeper are used for space launch vehicles, which are permitted under START I.

On 24 August the United States announced the destruction of the last Minuteman III silo at Grand Forks, North Dakota.

On 30 October, Ukraine completed its compliance obligation under the START I Treaty by destroying its last SS-24 ICBM silo.

On 13 November President Putin announced that in late October the last Ukrainian nuclear warhead had been destroyed in Russia.

On 5 December the United States and Russia announced that both parties had fulfilled START I requirements. In particular, Russia announced that it had reduced its deployed strategic delivery vehicles to 1136 and its accountable warheads to 5518. This accomplishment marked the largest arms control reduction in history.


In congruence with START I obligations, on 22 December the United States announced that the last Minuteman II silo was destroyed at Whiteman Air Force Base.


On 23 November, after transferring its remaining ICBMs and nuclear warheads to Russia, Belarus announced that it had fulfilled its START I and NPT obligations and officially became a non-nuclear-weapon State.


On March 14 a Russian Defense Ministry spokesman announced that US START I verification inspectors were “satisfied” with the three ICBM bases that they inspected during the first round of inspections conducted under the START I regime. The inspectors examined the Kostroma SS-24 base, the Irkutsk SS-25 base, and the Yasnaya SS-25 base.

On 9 November, a revision of the START I treaty was signed in Geneva, allowing converted mobile strategic missiles to be used as space launchers. Under the revision, Russia can establish space-launch sites anywhere in the world as long as the converted ICBM launchers remain under Russian control.

On 1 March, three 10-member teams from the On-Site Inspection Agency arrived in Russia from the U.S. to begin a 120-day baseline inspection. The teams inspected 71 weapons facilities in Belarus, Kazakhstan, Russia, and Ukraine.


On 5 December at the Budapest Conference on Security and Cooperation in Europe, the United States, Belarus, Kazakhstan, Russia and Ukraine exchanged instruments of ratification for START I, thereby marking the treaty’s entry into force.

In May, the Joint Commission on Inspection and Compliance met in Geneva to discuss the implementation details of START I. Representatives from the United States, Belarus, Kazakhstan, Russia and Ukraine signed several agreements that will help to realize the multilateral obligations of START I.


On 26 November the Russian government formally denounced the Ukrainian Rada’s conditional ratification of the START I Treaty, stating that it was not valid under international law.

On 18 November the Ukrainian Parliament ratified START I and the Lisbon Protocol. However, given Ukraine’s serious reservations about the Treaties, doubts arose concerning Ukraine’s commitment to the NPT as a non-nuclear weapon state.

On 2 July Kazakhstan ratified START I and subsequently acceded to the NPT as a non-nuclear weapon state on 14 February 1994.

On 23 April, President Clinton announced an accelerated reduction schedule for U.S. strategic forces under START I in an attempt to further strengthen disarmament and security measures.

On 4 February, Belarus ratified START I, the Lisbon Protocol and acceded to the NPT.


On 4 November, Russia ratified START I. However, Russia announced that it would not exchange its instrument of ratification until Belarus, Kazakhstan and Ukraine were to accede to the NPT as non-nuclear weapon states.

On 23 May, the United States, Belarus, Kazakhstan, Russia and Ukraine signed the Lisbon Protocol in Portugal. Furthermore, Belarus, Kazakhstan and Ukraine agreed to accede to the NPT as non-nuclear weapon states in “the shortest possible time”.


On 31 July, President Bush and President Gorbachev signed START I. The Treaty was expected to cut strategic warheads arsenals by approximately 35%.

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Strategic nuclear warhead
Strategic nuclear warhead: A high-yield nuclear warhead placed on a long-range delivery system, such as a land-based intercontinental ballistic missile (ICBMs), a submarine-launched ballistic missile (SLBMs), or a strategic bomber.
Intermediate-Range Nuclear Forces (INF) Treaty
A treaty between the United States and the former Soviet Union, signed on 8 December 1987, which entered into force on 1 June 1988. It aimed to eliminate and ban all ground-launched ballistic and cruise missiles with a range of between 300 and 3,400 miles (500 to 5,500 kilometers). The treaty required the United States and the Soviet Union to conduct inspections at each other's sites during the elimination of treaty-limited items (TLI). By May 1991, all intermediate-range and shorter-range missiles, launchers, related support equipment, and support structures were eliminated. For additional information, see the INF Treaty.
Non-nuclear weapon state (NNWS)
Non-nuclear weapon state (NNWS): Under the Treaty on the Non-Proliferation of Nuclear Weapons (NPT), NNWS are states that had not detonated a nuclear device prior to 1 January 1967, and who agree in joining the NPT to refrain from pursuing nuclear weapons (that is, all state parties to the NPT other than the United States, the Soviet Union/Russia, the United Kingdom, France, and China).
Strategic Arms Reduction Treaty (START I, II, & III)
Refers to negotiations between the United States and the Soviet Union/Russian Federation, held between 1982 and 1993 to limit and reduce the numbers of strategic offensive nuclear weapons in each country’s nuclear arsenal. The talks culminated in the 1991 START I Treaty, which entered into force in December 1994, and the 1993 START II Treaty. Although START II was ratified by the two countries, it never entered into force. In 1997, U.S. President Bill Clinton and Russian President Boris Yeltsin discussed the possibility of a START III treaty to make further weapons reductions, but negotiations resulted in a stalemate. Following the U.S. withdrawal from the Anti-Ballistic Missile Treaty (ABM) in 2002, Russia declared START II void. START I expired on 5 December 2009, and was followed by the New START treaty. See entries for New START and the Trilateral Statement. For additional information, see the entries for START I, START II, and New START
National technical means (NTM)
NTM: Satellites, aircraft, electronic, and seismic monitoring devices used to monitor the activities of other states, including treaty compliance and movement of troops and equipment. Some agreements include measures that explicitly prohibit tampering with other parties' NTM. See entries for Transparency measures and Verification.
Cooperative Threat Reduction (Nunn-Lugar) Program
A U.S. Department of Defense (DOD) program established in 1992 by the U.S. Congress, through legislation sponsored primarily by Senators Sam Nunn and Richard Lugar. It is the largest and most diverse U.S. program addressing former Soviet Union weapons of mass destruction threats. The program has focused primarily on: (1) destroying vehicles for delivering nuclear weapons (e.g., missiles and aircraft), their launchers (such as silos and submarines), and their related facilities; (2) securing former Soviet nuclear weapons and their components; and (3) destroying Russian chemical weapons. The term is often used generically to refer to all U.S. nonproliferation programs in the former Soviet Union—and sometimes beyond— including those implemented by the U.S. Departments of Energy, Commerce, and State. The program’s scope has expanded to include threat reduction efforts in geographical areas outside the Former Soviet Union.


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