Able Archer 83 is the closest the world has come to nuclear war since the Cuban Missile Crisis. The early 1980s was a period of major tensions between the Soviets and the Americans, as Reagan called for the creation of the SDI and deployed Pershing II missiles to Europe. In the middle of these tensions NATO decided to hold a series of wargames simulating the escalation of a global crisis up to DEFCON 1, culminating in a simulated nuclear attack. The Soviets were worried about a first strike attack by the new Pershing II missiles and thought that a nuclear attack was most likely to occur during war games or a military exercise. As part of Operation RYAN the Soviets had infiltrated agents into the NATO nuclear command and control apparatus but the spies were only ordered to report their observations, not their analysis of the situation. When the Operation RYAN agents started noticing preparations for a nuclear attack and when Soviet signals intelligence started noticing increased encrypted communication between the US and UK (thought to be sharing information for an attack, actually communication regarding the Invasion of Grenada) and NATO switching to classified communications channels it fit into Soviet views of what a nuclear attack would look like. Since Soviet doctrine always relied on a nuclear exchange prior to initiating conventional war (and always thought the US had the same doctrine) all it takes is for the Soviets to decide to hit NATO first for a nuclear exchange to occur.