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A period of deÂtente between the USA and the Soviet Union (formally, the Union of Soviet Socialist RepublicsÐUSSR) allowed for the first serious negotiations on arms control between the superpowers to commence in 1969. A coincidence of different motives made for relatively easy and rapid progress. The USA wished to avoid an expensive arms race with the USSR, in part because it was heavily involved in the financially ruinous Vietnam War. Furthermore it was very much in the USA's interest to have the USSR remain relatively passive while it was so heavily engaged in South-East Asia. The USSR had been seeking nuclear parity with the USA ever since the Cuban missile crisis of 1962, and could not hope to achieve this if the USA was to continue increasing its missile stock. Even given this no agreement could have been achieved but for a specific fact about strategic nuclear war. At least according to the US theory of mutual assured destruction, nuclear weapons were unlike conventional arms because there was an upper limit to the number of warheads that could possibly be needed. The USA believed that its nuclear inventory had already reached such a level, and that adding to it would not give any added security, so were prepared to agree to some form of parity with the USSR. The SALT I Treaty (technically the Interim Agreement on Strategic Offensive Arms), signed in 1972, was, however, very limited because of verification problems. Neither country was prepared to allow onsite inspection, so verification had to be limited to what are known as `national technical means'. This essentially meant reconnaissance satellites, which could do little more than count the total numbers of missile silos or, as SALT I's critics put it, `holes in the ground'. Very little could be ascertained about the technology installed in the missiles, and even less about submarine-launched ballistic missiles (SLBMs). Nevertheless, SALT I brought a degree of stability by putting an upper limit on the total number of missiles each country could have, based roughly on existing US force levels. SALT I was always intended as a temporary holding operation, to be completed in a more ambitious way by a second treaty, on which negotiations started immediately. The Anti-Ballistic

Missile (ABM) Treaty was negotiated and signed as part of the same procedure. A second treaty, SALT II, was ready for signing by 1979, and dealt more

specifically with the total numbers and explosive power of warheads, rather than with the mere delivery systems limited under SALT I. It took account of the new technology of MIRV (multiple independently-targeted re-entry vehicle) warheads that SALT I had ignored. Since the development of this technology in the late 1960s the number of missiles had become much less important because each missile could carry up to a dozen, or even more, separate warheads. Little could be done to control the total number of these precisely, and negotiations proceeded obliquely by calculating the maximum number of warheads a missile of a given thrust and size could theoretically carry, and assuming that all missiles would carry this maximum. At the same time as the SALT II negotiations were taking place deployment of another new technology, the slow, low-flying, but very sophisticated, cruise missile, was being planned. Although outside the remit of the SALT procedure, as they were non-strategic, cruise missiles could not be ignored as they could be launched from ground, air, ship or submarine, and travel several thousand miles; although their main purpose was against battlefield targets, they could also theoretically be used against strategic targets. (Ground-launched cruise missiles only came under control later in the politically very different context of the Intermediate Nuclear Forces (INF) Treaty.) The SALT II Treaty was successfully negotiated despite these difficulties,

although the limits agreed on allowed the number and sophistication of weapons on both sides to increase considerably. It was, however, never ratified because the USSR's invasion of Afghanistan, combined with unrelated political opposition to the USSR in domestic US politics, forced President Jimmy Carter to withdraw it from Senate consideration. Despite this both sides agreed to abide by it and, to a very large extent its limits were followed, despite a collapse of deÂtente after Ronald Reagan's accession to the presidency in 1981, past its proposed expiry date of the end of 1985 and until the whole atmosphere of superpower arms control negotiations had changed in the late 1980s.