The Rocketdyne S-3D (Air Force designation LR79)[1][2] is an American liquid rocket engine produced by Rocketdyne (a division of North American Aviation) between 1956 and 1961.

It was a gas generator, pump-fed engine, using a liquid oxygen (LOX) and RP-1 (kerosene) propellant combination, capable of producing 134908 pounds of thrust (600.1 kN) at sea level.

[3] The S-3 was based on the Redstone engine,[4] and is part of LR79 family,[5][6][1][2] used on the PGM-19 Jupiter and PGM-17 Thor missiles,[7][4][8] and on the Juno II rocket.

[3][9][10][11] A second stage with four S-3 engines was considered for the Saturn A-2 study.

[12] Its design was used later as the basis for the H-1 rocket engine of the Saturn I,[13][1][7] and the Rolls-Royce RZ.2 of the Blue Streak.