The Cuban Missile Crisis
Tensions between the two governments peaked again during the October 1962 Cuban missile crisis. The United States had a much larger arsenal of long-range nuclear weapons than the Soviet Union, as well as medium-range ballistic missiles (MRBMs) in Turkey, whereas the Soviet Union had a large stockpile of medium-range nuclear weapons which were primarily located in Europe. Cuba agreed to let the Soviets secretly place SS-4 Sandal and SS-5 Skean MRBMs on their territory. Reports from inside Cuba to exile sources questioned the need for large amounts of ice going to rural areas, which led to the discovery of the missiles, confirmed by Lockheed U-2 photos.
The United States responded by establishing a cordon in international waters to stop Soviet ships from bringing in more missiles (designated a quarantine rather than a blockade to avoid issues with international law). At the same time, Castro was getting a little too extreme for the liking of Moscow, so at the last moment the Soviets called back their ships. In addition, they agreed to remove the missiles already there in exchange for an agreement that the United States would not invade Cuba. Only after the fall of the Soviet Union was it revealed that another part of the agreement was the removal of US missiles from Turkey.
It also turned out that some submarines that the US Navy blocked were carrying nuclear missiles and that communication with Moscow was tenuous, effectively leaving the decision of firing the missiles at the discretion of the captains of those submarines. In addition, following the dissolution of the Soviet Union, the Russian government revealed that FROGs (Free Rocket Over Ground) armed with nuclear warheads and Ilyushin Il-28 Beagle bombers armed with nuclear bombs had also been deployed in Cuba.