In 1971, Douglas won a competition to provide jet transport aircraft to the U.S. Navy in the form of a convertible version of the DC-9-30. The aircraft featured a main deck cargo door on the left forward fuselage. While similar to the Air Force’s C-9A Nightingale Medevac version of the DC-9, the Navy version had enough differences in both mission and configuration to warrant a separate designation and name – C-9B Skytrain II. Eventually, 16 new-build C-9Bs were delivered, with two going directly to the Marine Corps. In addition to the 14 true C-9Bs, the Navy would later acquire 17 second-hand civilian DC-9s to supplement its fleet. Most of these DC-9s were -F or -CF aircraft with main deck cargo doors, but 4 were pure passenger aircraft with no cargo door.