You're talking the Cuban Missile Crisis. Ask yourself this, did missiles threaten the actual security of the Soviet Union? Did the missiles present a threat to Khrushchev? The Soviet missiles placed in Cuba were a direct response to the US missiles placed in Turkey. Khrushchev saw the Jupiter IRBMs (Intermediate-Range Ballistic Missiles) in Turkey as a real threat to the Soviet Union. The Soviets had MRBMs (Medium-Range Ballistic Missiles) and IRBMs in the USSR but their range meant they could only wipe out Alaska. They were a real threat to the residents of the 49th state, but the lower 48 didn't have to worry. US missiles in Turkey meant that in the event of a war breaking out between the US and USSR that the US could wipe out Moscow in a nuclear missile strike while the USSR couldn't touch Washington DC. Placing R-12 MRBMs and R-14 IRBMs in Cuba gave the Soviet the ability to threaten not only Washington DC but much of the eastern seaboard.