Securing insight into foreign scientific and technical developments has always been a significant priority for spies – just as important as protecting a home nation's own engineering developments. Intelligence, weapons proliferation and counter-proliferation have historically been closely related. Intelligence was, in several senses, crucial to the development of the Cold War superpower nuclear arms race. The relentless intelligence effort of the USSR's intelligence services yielded the secrets of the Manhattan Project, easing Stalin's development of his first atomic bomb. Thereafter, all sides expended tremendous effort to understand the adversary's nuclear infrastructure and gauge their capabilities and intentions. But as the twentieth century progressed and the superpowers shifted, incrementally and stutteringly, from arms races to a degree of arms control, the intelligence machinery found another role beyond espionage and counter-intelligence: namely, monitoring and verification.

For at least the first twenty years of the Cold War, the US enjoyed a marked strategic advantage over the USSR. Despite certain key instances where the Soviets had stolen a march in developing strategic systems, such as developing versions of intercontinental bombers in the 1950s, or testing their first ICBM before the US in August 1957, these gains were soon offset. The US, with its NATO allies, compensated for any lag in long-range strategic capability by deploying shorter-range assets in Europe, closer to the USSR; and they soon developed their own ICBMs and intercontinental bombers and proceeded to build more of them more quickly than the USSR. Despite fears of a strategic imbalance in favour of the Soviets in the 1950s, most notably manifested in the bomber and missile ‘gap’ controversies as discussed in Chapter 6, by the 1960s the US retained this lead. US intelligence could, essentially, prove this beyond reasonable doubt owing to the rapid development of overhead reconnaissance technology: first the U-2 high-altitude aircraft from 1956, and then the CORONA reconnaissance satellite programme after 1961. This intelligence was supplemented by human sources, the most significant being GRU Colonel Oleg Penkovsky (introduced in Chapter 7), who was recruited by SIS and run in partnership with the CIA. Penkovsky provided detailed information on the Soviet strategic rocket programme, before being identified and executed.