The iconic Douglas DC-9 airliner was chosen by the USAF for a aeromedical evacuation and VIP transport aircraft as the C-9A and VC-9C respectively and by the US Navy/USMC as a passenger/cargo aircraft as the C-9B. 21 C-9As and 3 VC-9Cs were built for the USAF, while 17 C-9Bs were built for the USN/USMC as well as 14 ex-civil airliners that were leased and or purchased by the Navy. Many of the purchased DC-9s were converted to C-9B standards with the addition of a large cargo loading door on the forward left-hand side of the fuselage. A 32nd C-9B was purchased through the Navy but operated by the US government and later by Ratheon as a NC-9D. Two other C-9Bs were purchased through the Navy for Kuwait and one Navy C-9B was transferred to NASA as the "Vomit Comet" negative G test vehicle.