Atlas

The first ICBM to go on operational alert for the U.S., starting in 1959, was the Atlas D rocket. (Pictured here is a 1958 Atlas test launch.)

"The time was right," retired Brig. Gen. Elmer Brooks is quoted as saying in an Air Force public affairs release ahead of this month's 50th ICBM anniversary. "The U.S. was engaged in a tense Cold War and an arms race with the U.S.S.R. Rocket, guidance, and nuclear warhead technologies matured to the extent that combining them in an ICBM was feasible. ICBMs provided the capability to strike targets with a nuclear bomb virtually anywhere in the world within 35 minutes of launch with no known defenses."