MSC's Director of Flight Crew Operations Donald K. Slayton said that the Block I flight crew nomenclature was suitable for the AS-204 mission, but that a more descriptive designation was desirable for Block II flights.

Block I crewmen had been called command pilot, senior pilot, and pilot. Slayton proposed that for the Block II missions the following designations and positions be used: commander, left seat at launch with center seat optional for the remainder of the CSM mission, and left seat in the LM; CSM pilot, center seat at launch with left seat optional for remainder of mission; and LM pilot in the right seat of both the CSM and LM.