The 737 based C-40 Clipper represents a substantial upgrade over the 1970s-era, DC-9 based C-9 Skytrains and 727-based C-22Bs that have performed its transport roles to date. The C-9s are still in service with the US Naval Reserve and USAF, but they’re expected to be be phased out as the C-40s take up the load. Meanwhile, concern has been expressed about the funding levels for this replacement program, as well as the USAF and US Navy C-9 fleet’s continued durability. The USAF’s C-9A models are of particular concern.
The C-40 comes in 3 variants; the C-40A is a Navy aircraft, while its counterpart C-40C and executive/ VIP C-40Bs are USAF planes. The USAF’s C-40 leasing contracts have been a source of some controversy, but the program has continued, alongside Air Force and Navy buys.