Saturn A-1, studied in 1959, was projected to be the first version of Saturn I and was to be used if necessary before the S-IV liquid hydrogen second stage became available. It was proposed as a launcher for Project Horizon, a scientific / military base on the Moon project, at a time when the U.S. Department of the Army, Department of the Navy, and Department of the Air Force had total responsibility for U.S. space program plans.
The rocket was designed as a three stage vehicle. The S-I first stage (initially proposed for the Juno V rocket and eventually used on Saturn I) with eight H-1 engines would propel the Saturn A-1 into space, continuing the flight with a Titan I missile based second stage with two LR-87-3 engines. Finally a Centaur C high-energy double RL-10A-1 engine third stage could send a payload into its final Earth orbit or to other planets.
The Saturn A-1 never flew, but all proposed stages were used on different launch vehicles. Today, they are all retired.
See also
S-I Saturn I Juno V Titan I Centaur Project Horizon
References