C-131G respectively. A number of R4Y-1 (C-131F) aircraft were converted to R4Y-1Z (VC-131F) or R4Y-2 (C-131G) standards after delivery, and several C-131F and C-131G aircraft were ultimately sold as military surplus and converted to civil use. Nearly all of the C-131s left the active USAF inventory in the late 1970s, but the U.S. Coast Guard (USCG) operated the aircraft until 1983, while the Air National Guard (ANG) and USN units operated additional C-131 airframes, primarily as Operational Support Aircraft (OSA) for ANG flying wings and as naval air station "station aircraft" until 1990. The C-131 was primarily replaced by the C-9 Nightingale in regular USAF service, with the ANG replacing their OSA with C-130 Hercules aircraft and the USN with C-12 Hurons. In 1959, a C-131 was the first aircraft to be used as a reduced-gravity aircraft or 'vomit comet', for astronaut training as part of Project Mercury. A Samaritan was the first aircraft used as a flying gunship testbed in mid-1963, in a program known as "Project Tailchaser". A C-131B (AF Ser. No. 53-7820) was given a gunsight for the side window, but instead of guns it had cameras in the cargo area. Eventually the C-131 was ferried to Eglin AFB in Florida and a General Electric SUU-11A/A 7.62 mm Gatling-style Minigun was installed. Live ammunition was used and both over-water and overland tests were successful. Accidents and incidents On 17 December 1960, a USAF C-131D Samaritan crashed at Munich after one engine lost power on takeoff from Munich-Riem Airport. Flying in heavy fog and unable to gain altitude, the aircraft struck the steeple of St. Paul's Church and crashed onto a tram, killing all 20 people on the aircraft and 32 on the tram. Variants C-131A Transport for USAF based on CV-240, capable of carrying 39 passengers on rearward facing seats, or 20 stretchers and 7 seats; 26 built. HC-131A Surplus C-131As transferred to the USCG, 22 transferred. MC-131A C-131A used for medivac duties with 27 stretchers. VC-131A C-131A used as a staff transport. C-131B A hybrid CV-240/340 with seats for 48 passengers, 36 built. JC-131B C-131B converted for missile tracking, six conversions. NC-131B One C-131B used for permanent testing. VC-131B C-131B when used as a staff transport. YC-131C Two CV-340s modified with Alison 501D-13 turboprop engines. C-131D Military version of the Model 340 with seats for 44 passengers, 33 built. VC-131D C-131D when used as a staff