Another line of development within the U.S. industry led, in the early 1950s, to the Navaho cruise missile. A cruise missile flies like an unpiloted aircraft to its target, rather than following the ballistic trajectory of an IRBM. This program was short-lived, but the rocket engine developed for Navaho, which itself was derived from the V-2 engine, was in turn adapted for use in a number of first-generation
ballistic missiles, including Thor, another IRBM, and Atlas and Titan, the first two U.S. ICBMs. A version of Atlas was used to launch John Glenn on the first U.S. orbital flight. The R7 was the first Russian ICBM.