Additionally, what was the NATO plan if Warsaw Pact forces went streaming through the Fulda Gap in an act of war?

edit:Thanks for all the help and answers!

I am sure there are awesome Soviet historians around here, but I will add the little bit that some of the more conspiratorially-minded during the first Red Scare in the U.S. and the West had stuff about the freshly revolutionized Russia, right after WW1, would spread communism through military means. To an extent, this was true, with the foreign-relations faction led by Trotsky advocating spreading the revolution to prevent containment of the revolution. The principle way of doing this was to connect with the incredibly unstable early Weimar Republic and its sizable Communist party (KPD), which had recently split from the largest socialist party up till, and really since, that point in time (SPD). This was the context of the Polish-Soviet War, were Poland was both an freshly-revived nation susceptible to a social change towards the left, and a direct land bridge to Germany. The KPD ultimately failed to prompt anything except the willingness of conservative elements to accept the social-democrats was a ruling coalition party at time, but in the upheavals all over Europe and North America of 1917-23, it was a distinct possibility, perhaps only for the fortunes of the Polish war, that Soviet-style communism (or a greater variety of socialisms supporting each other) could have "invaded" the West at the very beginning, and some like Trotsky and his notion of "permanent revolution" were pushing for that.

See: the huge amount of correspondence between the people like Lenin and Trotsky with groups like the Spartacist League (the precursor to the later KPD and founders of a Bavarian Soviet during the German revolution). Specifically, this letter from Trotsky to the Spartacists.

Some choice quotes from it:

"Since the argument relating to the illegitimate birth of the dictatorship of the Russian working class does not exercise any great influence upon the German workers, a new argument is now being advanced in order to traduce the Russian Revolution. The Soviet government is aiming, mind you, to invade Eastern Prussia with the Red Army. We don’t doubt that this fiction, too, which political charlatans are circulating in order to frighten and deceive idiots meets with no credence among German workers. It is our considered opinion that we shall fulfill our duty to the international revolution if we preserve the rule of the working class on the soil of Russia..."

"We send to the German proletarians our fervent greetings and ask them to believe that never have they been so close and dear to the heart of every Russian Communist as they are today, when amid incredible hardships in the struggle against traitors and turn-coats, with the road dotted with lifeless bodies of their best fighters like Liebknecht and Luxemburg, they are tirelessly and courageously marching toward final victory."

For some Wikipedia reading, also consider the page on the Polish-Soviet War and Trotsky's "Permanent Revolution".

I know OP's request was obviously for Cold War-era stuff, but the origins of the Cold War are earlier than WW2 and in a way began ever since the Western powers intervention troops during the Russian Revolution. Plus, in the general theory of revolutionary communism, there is always plan of "invasion," because the hope is you can support the foreign proletariat in his revolutionary efforts; i.e. the nationalist identification required for most definitions of "invasion" can widen the question. Plus my focus is on German history and Marxist political-economic theory, so its all I could speak on. :)

Hope I'm not too late here. I'm a documentary filmmaker and have been working on a project that explores the various plans for an East-West military conflict during the Cold War. The most valuable source I have found for this is Siegfried Lautsch's book "Kriegsschauplatz Deutschland" (Battleground Germany). It's German, but very interesting and very good, and goes into a great deal more detail than the usual "Fulda Gap" articles you find online.

The set pieces needed for such an attack were in place nearly permanently. The Soviet Union had 7 armies stationed within East Germany, the East German army had 2 additional "armies" (they were called "military districts" in peace time) and could mobilize additonal forces. Among the Soviet armies were several elite formations (such as the 1st Guards Tank Army and the 3rd Shock Army). This does not include additional forces that could strike West from within Czechoslovakia, so we're talking about an even bigger amount of forces that were available on very short notices.

In addition, the Soviet troops in Germany were usually supplied with the newest and best military hardware.

While the composition of troops changed during the course of the Cold War, it's safe to say that the set pieces needed for a large-scale invasion of West Germany (and, following, Western Europe) were very much in place.

As for specific plans, there were many variations of an attack, the majority of with (that I know of, or have seen) focused on an attack through the so-called Fulda gap. They varied in the timing, in which forces were to be used, the operational limits, etc. - but this was seen, by both sides, as vital to military success.

The US was concerned about a Soviet invasion of Western Europe because its ability to counter it was limited. It had large amounts of materiel stationed in Western Europe, but not the troops that were needed to use it. The plan was to ship troops into Europe as quickly as possible if War broke out, and thus have the ability to withstand a Soviet attack.

This plan, however, had one big problem. If the Soviets were able to strike the depots where tanks, etc. were housed (there were plans for this, ranging from conventional bombardment, to chemical and nuclear weapons), the war would be lost before it even began.

As for the American nuclear option - this was seen as being of limited use. If the US employed theater nuclear weapons (that is, tactical warheads, which might be dropped on invading Soviet armies and stop their advance), this could easily lead into an exchange where Soviet nuclear missiles would fly at the US. Given this scenario, it would have made more sense for the US to give up Western Europe entirely. This was the prime reason, for example, that France sought to have nuclear weapons of its own, since it did not trust that the US would make good on their promise to use nuclear weapons in support of Europe.

Follow up question: I have read many times that the Soviet leaders, Gorbatsjov in particular, where absolutetely dreading a NATO invasion, one they believed could not be won. The postering and arms buildup was to deter from invasion.

apparently this doctrine was found in released documents.

Is there any truth to this?

Related question - how accurate was The Third World War by Sir John Winthrop Hackett? I know it was a fictionalized version of a land war in Europe and it's been 30 years since I read it.