(Historic Spacecraft)"/>The Thor-Delta family was one of the earliest United States launch vehicles. The earliest Thor was derived from the PGM-17 Thor Intermediate-Range Ballistic Missile (IRBM). The Thor-Delta family of vehicles has seen many iterations from the earliest Thor-Able launches of 1958 to the advanced Delta IV that is still in use today.
The first vehicle called Delta was the Thor-Delta launched in 1960.