Nuclear doomsday scenarios in the 1960s set off an arms race with the Soviets rather than disarmament.

The test has two parts: whether the 1960s saw an arms race with the Soviets rather than disarmament, and whether nuclear doomsday scenarios drove it. TRUE: historical scholarship shows that 1960s nuclear doomsday warnings or scenarios fed escalation of the US–Soviet arms race, and that no meaningful disarmament followed. MOSTLY TRUE: the arms race clearly escalated in the 1960s and doomsday fears plausibly contributed, but the decade also saw limited arms-control steps (e.g. the 1963 Partial Test Ban Treaty, the 1968 NPT) that fell short of disarmament. MIXED: the arms race continued, but historians mostly attribute it to other causes (strategic competition, the missile gap), or arms control was a substantial counter-trend. MOSTLY FALSE: the arms race predates and is independent of the doomsday scenarios, and the causal link is stated without support. FALSE: the 1960s saw substantial nuclear disarmament rather than an arms race.

Set before the research began.

1. E1 Nuclear competition in an era of stalemate, 1963–1975 (Chapter 5) - The Cambridge History of the Cold War Cambridge University Press · 28 September 2010

   “During the 1960s, the United States deployed over a thousand intercontinental ballistic missiles (ICBM), hundreds of submarine-launched ballistic missiles (SLBMs), and took the arms race in a new qualitative direction by developing accurate multiple independently targetable re-entry vehicles (MIRVs).”

2. E2 20th-century international relations - Cuban Missile Crisis, Cold War, Superpowers | Britannica Encyclopaedia Britannica · 26 July 1999

   “None of the arms-control instruments of the 1960s, however, put a cap on the arms race or restrained the signatories from doing anything in the strategic area they had a desire to do anyway.”

3. E3 The Missile Gap Myth and Its Progeny Arms Control Association (Arms Control Today) · 3 May 2011

   “What was then labeled “the missile gap” also helped establish patterns in the nuclear arms race that persisted throughout the Cold War and beyond.”

4. E4 Imagining Armageddon: Herman Kahn's nuclear ladder Prospect Magazine · 19 July 2023

   “By the end of the 1950s he had risen to infamy, when it appeared that the Soviet Union’s nuclear armament programme was catching up with America’s.”

E1 records a large US build-up during the 1960s: over a thousand ICBMs, hundreds of SLBMs and the development of MIRVs. E2 says none of the decade's arms-control agreements capped the arms race, so the part of the claim about "an arms race, not disarmament" is supported. None of the evidence links the arms race to doomsday scenarios. E3 says what was labelled 'the missile gap' helped establish lasting patterns in the arms race, and E4 says only that Herman Kahn rose to infamy when it appeared Soviet armament was catching up with America's, not that doomsday scenarios drove the escalation. Because the evidence links the arms race's patterns to the missile gap [E3] and none of it ties the arms race to doomsday scenarios, this meets the criteria for mixed.