Beginning with the first manned U-2 flight in 1956 and culminating with satellite missions that produced detailed images of the vast Soviet landmass, the "eyes in the sky" closely monitored Soviet missile and atomic programs, permitting arms-limitation agreements that truly benefited all of mankind.
Sometimes we think of military intelligence as part of war, but it is much more about keeping peace. Rather than win a war, it is better to make sure that the war never happens in the first place, and that's largely what happened between the United States and the Soviet Union. Much of the airborne surveillance was organized by President Eisenhower,
whose repugnance at the thought of a nuclear war led him to push for the overflight programs even though he realized the risk of provoking a confrontation with the Soviets. As Richard Helms, the director of central intelligence, later summarized, "For the first time, American policymakers had accurate, credible information on Soviet strategic assets ... It was the greatest bargain and the greatest triumph of the Cold War."
Eisenhower knew that a nuclear war would be unspeakable horrible, and that the full power of military intelligence could save the human race from this frightfulness. Keeping millions of families peacefully safe, however, had its price.
The flights were highly dangerous. Crew members, chiefly drawn from the Air Force and Navy and their signal units, were briefed on the perils involved. According to a National Security Agency historian, "Of the 152 cryptologists who lost their lives during the Cold War, 64 were engaged in aerial reconnaissance." Families of the downed airmen were never told what happened to them, only that they had been on "secret missions."
Of course, out of all the spy pilots shot down, not all of them died. The most famous pilot was captured alive: Francis Gary Powers. He airplane was attacked by Soviet defenses on May 1, 1960. He was taken prisoner as he parachuted to safety. Although the Soviets pretended to be shocked and offended by the fact that the United States was taking photographs over their land, they were in fact even more active in spying on us: their network of on-the-ground spies in America exceeded any activity we managed to organize in Russia.
The Cold War is now over, and we were saved from having to face a nuclear war by the sophistication and bravery of military intelligence gathering.