Combat!

From TeeVeePedia, the Internet TV Encyclopedia.

Combat! was a reality show on ABC in which contestants, all young men ages 18-27, competed for a chance to join the cast of Vietnam War. The show was a huge hit when it debuted in 1962, but by 1967 interest in Vietnam War had waned to the point where the producers could no longer attract enough interesting contestants, and the show was cancelled.

McLean Stevenson proposed a new version of Combat in 1975, but it never lept.