While it was being developed, Heinz-Hermann Koelle at the Army Ballistic Missile Agency (ABMA) selected it as the primary engine for the rocket that would emerge as the Saturn I.
Atlas used a number of unconventional features in order to meet its performance goals, and they felt that there was undue risk that if any of these proved unworkable in practice then the entire design would fail.
Based on these reports, Ramo suggested that the Air Force begin development of a new missile that used a conventional airframe in place of the Atlas's "balloon tanks", and replaced the "stage and a half" layout with a two-stage design.
Starting with the basic layout from their successful MB-3/S-3 (known to the Air Force as the LR79) from the Thor and Jupiter missiles, Rocketdyne developed the E-1 by expanding its size and tuning the engine bell for operation at lower altitudes.
[3] In April 1957 Wernher von Braun tasked Heinz-Hermann Koelle with the development of a space launch system to meet new requirements specified by the then-unofficial ARPA.
Koelle concluded that in order to meet their payload requirements, 10,000 to 20,000 lb (9,100 kg) into low Earth orbit, a booster stage with 1 million pounds of thrust would be needed.
To speed development of Juno V, the engines were attached to a single thrust plate, and supplied propellant from a cluster of tanks taken from the existing Jupiter and Redstone missile airframes.
The Army had already lost interest in the development of the Saturn due to a lack of mission requirements, and had agreed to turn over the ABMA team to NASA on 1 July 1960.
[3] When Aerojet successfully demonstrated the LR-87, the Titan moved ahead with this engine and the first production example was delivered to the Air Force in 1958.