Oplans 316 and 312 – US Invasion of Cuba in 1962
During the Cuban Missile Crisis in 1962, the Pentagon urged President Kennedy to invade Cuba in order to remove Soviet nuclear missiles from the island, and the Joint Chiefs of Staff unanimously agreed that a full-scale invasion was the only solution. They presented the Presidents with two versions: Oplan 316 for a full invasion, and Oplan 312 for aerial strikes to take out the missiles, followed by an invasion if necessary. The hawks, led by Air Force General Curtis LeMay, had a clear preference for Oplan 316, as they contended that there was no guarantee that airstrikes alone would take out all the missiles, or that one or more of the missiles would not be fired at the US.
Planners expected 18,500 US casualties in the first ten days of the invasion, assuming no nuclear explosions. However, unbeknownst to planners, the Soviet forces in Cuba had tactical nuclear weapons, and Soviet leader Nikita Khrushchev had preauthorized the Soviet commander in Cuba to use tactical nukes at his discretion if he deemed it necessary. As the crisis intensified, Khrushchev withdrew release authority and forbade their use without his express permission. However, whether the modified orders would have been followed, is debatable.
In practice, tactical nukes were dispersed throughout Cuba to various Soviet units, under the physical control of officers as low down the chain of command as captains. Soviet forces had drilled in the use of those weapons as part of their defensive plan, and in the heat of battle, the custodians of those weapons would have been under intense pressure as they were subjected to overwhelming US aerial strikes, naval bombardment, and ground attacks. It is not difficult to envision a desperate local commander in such a scenario, perhaps cut off from communications with higher authority, resorting to the tactical nukes at hand to save his command, or at least ensure that its demise did not come cheap: the Red Army, with victory in WWII only 17 years in its past, did not lack military pride or an ethos of defiance unto death.
If the Soviets used nukes in Cuba, the US intended an overwhelming nuclear response. Things could easily have escalated from there to a full-blown nuclear exchange that would have devastated both countries and Europe, irradiated the Northern Hemisphere, and set humanity back centuries. Luckily, President Kennedy resisted the pressure from his generals and admirals and relying on diplomacy, back channels, and blockade, successfully diffused the crisis without triggering WWIII.