In December 1957, ABMA delivered "Proposal: A National Integrated Missile and Space Vehicle Development Program" to the DoD, detailing their clustered approach. They proposed a booster consisting of a Jupiter missile airframe surrounded by eight Redstones acting as tankage, a thrust plate at the bottom, and four Rocketdyne E-1 engines, each having of thrust. The ABMA team also left the design open to future expansion with a single engine, which would require relatively minor changes to the design. The upper stage was the lengthened Titan, with the Centaur on top. The result was a very tall and skinny rocket, quite different from the Saturn that eventually emerged.