In light of Noung's excellent historical overview above, it's worth briefly focussing on the social implications this period had in the UK.
Able Archer 83 was the centerpiece of a period of intense British nuclear paranoia. It was extremely fortunate for the UK government that this event didn't enter the public consciousness until years afterward, such was the degree of public concern. In order to explain this to foreigners, one key fact about the United Kingdom needs to be focused upon - Britain is really, really small.
Popular nuclear paranoia can be seen as going through three main phases over the course of the Cold War. In the early 1950's conventional fission bombs were the perceived primary threat, and neither side had a sufficiently developed arsenal of bombs or ICBMs (first fielded in 1959) to make mutually assured destruction a valid strategy. This was the era of Duck and Cover (1951) when it was demonstrably feasible to survive in the peripheral range of a nuclear strike, and the need for bombers meant there was a potential for preparation and warning. However, it was also an era when radioactivity was a foreign, inexplicable concept with horrifying effects, intensely unsettling. In the later 1950's and throughout the 1960's this evolved into the Cuban Missile Crisis era, typified by On the Beach, when the invention of staged thermonuclear weapons meant nuclear war had become a catastrophic option. At this time the public was adjusting to the idea that war would result in annihilation and fallout. In Britain The War Game(1) (1965), a banned BBC fictionalised documentary, gives a clear insight into popular perceptions of the outcome of a nuclear strike. While horrific, it's notable that The War Game is by later standards reasonably low key, the UK is described as having "approximately 60 nuclear targets" (that's a lot of quite small bombs for a country with an area of 0.1 million square miles) and the outcome of their suggested war was less than globally apocalyptic.
In the 1980's the technology of nuclear deterrence went through a significant upgrade; with the change from a Polaris system of submarine launched missiles (where sub-surface launched missiles were still of dubious reliability, and therefore launching ideally meant the vulnerability of surfacing the submarine), to the sophisticated Trident system of missiles and warheads that was virtually foolproof (finished in 1994). For Britain, this nuclear deterrent would mean a fleet of 4 Vanguard-class submarines, stationed near Glasgow, with one permanently at sea. To say this upgrade scared a portion of the British public would be a gross understatement. The British left, somewhat shell-shocked by PM Margaret Thatcher's tendency towards authoritarian militarism in the Falklands, Northern Ireland and the Iranian embassy siege, was less than comforted by the state's after-exchange agenda.
With a view to the substantial population (in the high 50 millions) and small area of country, along with the massive yield of a staged thermonuclear device, it became common currency to say that only 4-10 strikes would be required to render Britain defeated and virtually uninhabitable. Also, as one of Western Europe's two island nations, it wasn't under the same threat from conventional weapons as continental Europe. The result was the highest density of US military sites outside the traditional German flashpoint. It is only since the end of the Cold War that the rabbit-warren scale of British underground installations is apparent(3). Of the country's litter of abandoned nuclear defence facilities, the most illustrious is Hawthorn a 240 acre site under Corsham in Wiltshire. A fully fledged underground city this was intended as the long term base of The British Government. Now decommissioned this was not militarily sound after 1960, and it is likely that later and more sophisticated bases of equivalent scale are still location-classified. Britain was by the 1980's intended to be the key American outpost in Europe in the aftermath of a nuclear war.
It was against this backdrop that Reagan (elected over a year after Thatcher) began to crank up the tension levels between NATO and the Soviet Union. A portion of the British public became extremely upset. The environmental model of a nuclear winter was only developed in 1981 and this caught on, rapidly rendering Protect and Survive's helpful, mundane advice on food stockpiling and shelter construction a sad joke. The cultural output was formidable - the graphic novel When The Wind Blows, Alan Moore's V For Vendetta and the BBC fictionalised documentary Threads(4) (a timely and far bleaker update of The War Game) all tried to make the outcome of nuclear conflict a tangible possibility.
The Campaign For Nuclear Disarmament sprung from a minor pressure group with a membership of 4000 to a force capable of fielding vast numbers of protesters on the streets of London; the Labour Party - Britain's main opposition - felt the need to publicly wed itself to unilateral nuclear disarmament in order to ride this wave of ill-feeling. It is now apparent that this movement and its members evolved into what became modern environmental activism, explaining the sometimes hysterical tone of their debate and their relic resistance to nuclear energy production (nuclear hellfire is a topic that invites, nay demands, hysteria). At its highpoint, in October 1983 (less than a month before Able Archer 83), this movement managed to lead 300 000 concerned citizens to Hyde Park, the traditional focus of British protest, as part of 3 million brought that day to the capitals of Europe. This was the biggest demonstration the country had seen since the civil unrest of The Depression and it wouldn't be rivaled until the Iraq War and Fox Hunting protests of the Blair era. Young as I was, I was there.
Above Noung describes Reagan in terms of the relationship between peace and strength, but in the context of NATO his role was as first amongst equals. Thus the direct political implications for his allies in Europe are likely to have proved significant in the later choice to apparently "modulate" his tone. To the UK public at large the ramifications of this stick waving were already apparent. Much as was the case in the warm-up to the Iraq War the interpersonal intuition of human beings applied to their leaders (in the case of Iraq people mainly reacted to how Tony Blair's tone felt in their guts) is sufficient to interpret a situation that is supposedly classified, reading it more extensively than the supposedly better-informed commentariat suggested at the time. As was likely the case inside the Kremlin, the British people had built a personal relationship with Reagan's public persona, and were sufficiently concerned by what they saw to prepare for war. Able Archer must have been political dynamite for the Thatcher government, which would have been intimately involved in all activities of NATO. Should these events have passed into the public sphere, it seems unlikely the Thatcher government would have survived (the Westland Affair, a far smaller scandal a few years later, significantly shook the Conservative administration). Thus, while The Cuban Missile Crisis represents the highpoint of nuclear paranoia in the US, the largely unmarked Able Archer events are central to Europe's and Britain's history in relation to The Bomb. This was as high as the temperature of nuclear phobia ever got. It is a bizarre coincidence that while the people remained ignorant of the specific events, their attitude was right - even to the month.
Human beings are very, very good at reading each other... They read your manner, not your actions. Ignore this at your peril.
"Did Gordievsky's reporting bring home the message that the war scare in the Kremlin was serious and that it posed a potential danger of Soviet overreaction? ... Prime Minister Thatcher herself apparently delivered the chilling message to President Reagan, hoping to convince him to moderate his rhetoric and actions... Thatcher publicly urged a shift in policy on 29 September in an address at the annual dinner for the Churchill Foundation Award in Washington, where she knew her remarks would attract media--and White House--attention. Her theme--'we live on the same planet and must go on sharing it'--was a plea for a more accommodating Alliance policy." From A Cold War Conundrum: The 1983 Soviet War Scare by Benjamin Fleishcer, Oleg Gordievsky was the foremost British intelligence source in the KGB.
(1)The War Game can be viewed in its entirety on Google Video, due to certain legal quibbles over evading the banning order I suspect it is now fully in the public domain.
(2)Atomica is a British archive of civil defense material, where Protect and Survive can be read in its entirety.
(3) Subterranean Britannica is a fascinating internet archive of decomissioned British defence facilities, showing the scale of British combat-readiness.
(2)Threads can also be seen on Google Video, no idea why but its been there for 3 years. Eighties lefties probably aren't all that into intellectual property.