There were numerous strategies, based on all contingencies and situations the planners could come up with, but to understand how this came to be we're going to have to look into the history of nuclear planning.

Throughout the ages, wargaming and theoretical studies have enabled military planners to imagine different scenarios for different threats, which were then included in tactical and strategic plans for conventional warfare. During the Cold War, these generally took the form of: "If the Soviet Umpteenth Guards Division crosses into Western Germany HERE, and the Eleventeenth Rifle Brigade HERE, we can position our troops HERE and cut them off, then engage them with the 2743927th armored brigade!.". Things changed when nukes came into play...

When the USA started to field nuclear weapons in the late forties the initial plan was to use them for strategic purposes - as a substitute for the conventional, air delivered munitions used in such large quantities to destroy Hamburg, Tokyo and other cities. Generally, the nuclear bomb was seen as an ordinary bomb, only bigger, so they were included into the planning as such: "If we get attacked by those pesky Reds, we'll fly a couple of B-29's over Moscow and Leningrad and level those cities. That'll keep 'em away from us!". Probably a good idea, because the Red Army outnumbered the US Armed forces by a pretty large margin (in Europe at least) and this threat of nuclear devastation DID keep Stalin at bay. The nukes themselves had no tactical use however, because these weapons were huge, high maintenance monsters needing a lot of infrastructure. Not something you would want to leave in the hands of your average frontline soldier. Besides, it had to be dropped by a long range bomber which might take hours to reach its intended target - hardly ideal in a tactical setting. Even when the USSR detonated their first nuke in 1949, this did little to upset the USA - they had many more and much more capable methods of deployment.

So, during the early fifties, the USA had the USSR vastly outgunned in nukes but things were the other way round in men and tanks. In order to exploit this discrepancy, military theorists started to think about using nuclear weapons tactically - that means: "on the battlefield itself". The US came up with smaller bombs and short range, short response time delivery systems. These systems were integrated into operational doctrine and plans were updated along the lines of: "If the Soviet Umpteenth Guards Division crosses into Western Germany HERE, and the Eleventeenth Rifle Brigade HERE, we can launch a couple of Honest Johns HERE and vaporize them.". The USSR knew about this and they didn't like it a bit, but couldn't do anything about it due to the unequality in nukes and their delivery systems. "Tough cookies for you Ivan, deal with it! Hahahaha!"

But then the USSR started fielding nukes in earnest, and they put them into long range rockets. Then they went to the US and said: "Look here, I don't care what you say: a nuke ISN'T "an ordinary bomb, only bigger"! If you fire even a SINGLE nuclear weapon into our territory, we might have to strike back with everything we've got!". Yup, it turned out pretty much everyone everyone in the world except for a few hardcases in the US Armed Forces was feeling a bit uneasy about the ease with which tactical nuclear weapons had been fielded on a regional level. So, if the world thinks tactical use of nukes isn't a "Good Thing" at all, what in blazes CAN we use to keep the Soviets in Eastern Europe?

Almost immediately, the focal point of nuclear warfare switched back to the strategic realm once more, leaving the military theorists with the problem of "How the hell are we going to use these tactical nukes NOW?!". The trick was to "Integrate" both tactical and strategic nuclear "Operations" into a "Single" "Plan" - the "Single Integrated Operational Plan" or "SIOP". That's no mean feat, because the tactical and strategic realms are vastly different. The timeframes, the scope, the decisionmaking, all of these differ between these two. How can you make sure that a tactical decision doesn't impact global politics - or, if things really go to hell, global climate (nuclear winter)?

The USA and (presumably) the USSR came up with an escalation protocol which ultimately would lead to execution of the SIOP. This escalation ladder would take this form (from a NATO perspective): First operations were to be low level, conventional engagements aimed at local objectives. If these caused escalation, a higher level of operations including interdiction (=attacking enemy targets behind the frontline) was warranted. If these higher level of operations still didn't deter enemy action, a nuclear warning shot could be fired, consisting of a single nuclear weapon detonated at troop concentrations or choke points. If this STILL didn't deter the enemy (or caused retaliation in kind), "shit would be goin' down" and the SIOP goes into play, starting with nuclear strikes on tactical targets. These strikes were to be executed by NATO, not just the US - the Germans, Dutch and Belgians were (and are?) equipped with US-built nuclear weapons for this reason. By now, we're firmly into the strategic realm and we're within minutes of total nuclear war.