On July 25, 1962, NASA invited 11 firms to submit proposals for the LEM. Of the 11 invited, 9 submitted proposals. The firms that submitted proposals were Lockheed, Boeing, Northrop, Ling-Temco-Vought, Grumman, Douglas, General Dynamics Convair, Republic, and Martin Marietta. Grumman won.
Convair's proposed vehicle featured a single throttleable main engine backed by two standby thrust chambers. It was to be a partially staged configuration with a side-by-side crew arrangement and a probe-drogue docking mechanism. The lower structure held the descent tankage, which was to be depressurized 15 seconds prior to touchdown. The depressurized tankage, along with the crushable vehicle skirt, were to offer a back-up to the landing system in the event of a landing accident.
The engines were protected against landing damage through use of a crushable main engine nozzle skirt and the placement of the standby engines above the descent tankage. The reaction control thrusters were mounted on hinged arms, which folded 120 degrees to allow the vehicle to be stowed in the SIVB stage of the Saturn V rocket.
The concept was derived from studies of the probability of successful abort and complete mission success. Although the studies indicated that a multiple engine, two-stage vehicle had higher safety characteristics at higher levels of landing damage, Convair chose the stage and a half configuration due to the lower weight requirement.
Docking was to have been achieved by a probe and drogue mechanism. The method was to allow the crew to take advantage of good visibility and not have to change positions. Controls, displays and cues would not change during docking. Once the probe was aligned with the drogue, it would be locked in place, and the LEM rotated 90 degrees for final mating and crew transfer.