Under the treaty, the two countries have reduced their strategic nuclear arsenals by more than 40 percent over the past decade, decommissioning more than 4,000 strategic warheads since exchanging baseline stockpile information in September 1990. Reductions were implemented under a comprehensive monitoring and verification regime that included periodic information exchanges and intrusive monitoring and inspection provisions.
The accord requires Washington and Moscow to deploy no more than 1,600 long-range missiles and strategic bombers and caps deployed strategic warheads at 6,000, using rules that slightly undercount the number of warheads actually deployed. In addition, the countries must meet sublimits on ICBMs and submarine-launched ballistic missiles.
Signed by Presidents George H. W. Bush and Mikhail Gorbachev in July 1991, START I was the first treaty to substantially reduce the number of strategic nuclear weapons deployed by the United States and Soviet Union. The accord built on the first strategic arms pact between the two superpowers, an interim agreement that emerged from the Strategic Arms Limitation Talks in the early 1970s and capped—but did not reduce—the countries’ arsenals.
Shortly before leaving office, Bush also signed a START II agreement with Russian President Boris Yeltsin in January 1993. That agreement would have reduced U.S. and Russian arsenals to 3,500 deployed strategic warheads by 2007, but it has not entered into force, largely due to disagreements over U.S. national missile defense efforts.
In 1997 the United States and Russia also agreed to a framework for START III negotiations, which would have reduced the two sides’ strategic arsenals to 2,500 warheads by 2007. Under the framework, the two parties also agreed to consider measures to destroy their downloaded warheads and to increase the transparency of their strategic nuclear warhead inventories.
START I does not require the destruction of nuclear warheads removed from delivery vehicles; the United States and Russia have stockpiled substantial numbers of warheads as a result. Washington’s strategic and tactical warhead “hedge” is currently estimated at more than 5,000 warheads, while Moscow is estimated to have stockpiled more than 13,000 warheads.
The accord also does not cover nonstrategic nuclear weapons. The United States currently deploys an estimated 200-400 nuclear gravity bombs in Europe and stores, in operational condition, more than 1,000 additional tactical nuclear weapons. Experts estimate that Russia deploys about 3,500 tactical nuclear weapons.
The other three START I parties—Ukraine, Belarus, and Kazakhstan—all met their treaty obligations well in advance of the implementation deadline. These three states inherited nuclear weapons when the Soviet Union dissolved, only five months after START I had been signed. Under a May 1992 agreement, these states agreed to become parties to START I and to transfer all their nuclear warheads to Russia, a process completed by 1996. However, the three states retained most of the warheads’ strategic delivery vehicles—including both bombers and ICBMs—which the United States has helped them to destroy.
START I will remain in effect until December 5, 2009, during which time the treaty parties can request challenge inspections of suspect activity. The treaty parties also have the option to extend the accord for successive five-year periods if the treaty has not been superceded by another arms reduction agreement.