began phasing out its KC-97s in favor of the KC-135 Stratotanker. KC-97s continued flying with Tactical Air Command, the Air Force Reserve, and the Air National Guard. The rest of the KC-97s were retired completely in 1978, when the Texas Air National Guard and the Utah Air National Guard exchanged their KC-97Ls for the C-130 Hercules and the KC-135 Stratotanker, respectively. One KC-97 airframe (AF Ser. No. 52-0828) was adapted into the Aero Spacelines Super Guppy, a transport plane designed to carry Apollo Program rocket stages from California to Florida. The aircraft carried the Saturn S-IVB stage, which served as the second stage of the Saturn IB, the third stage of the Saturn V, and the fourth stage for the never-built Nova rocket. This modified KC-97, constructed in 1953, was eventually purchased by NASA in 1997. It is still in service supporting NASA, other Federal agencies, and Federal contractors. It is one of two KC-97s left still in flyable condition, the other being former KC-97G 52-2718, "Angel of Deliverance", currently flown by Berlin Airlift Historical Foundation as YC-97A 45-59595. Variants KC-97A Three C-97As were converted into aerial refueling tankers with rear loading door removed and a flight refueling boom added. After the design was proven, they were converted back into the standard C-97A. KC-97E aerial refueling tankers with rear loading doors permanently closed, 60 built. Some were later converted into transports as the C-97E. KC-97F 3800 hp R-4360-59B engines and minor changes, 159 built. Some were later converted into transport as the C-97F. KC-97G Dual-role aerial refueling tankers/cargo transportation aircraft. KC-97G models carried underwing fuel tanks. 592 built. EC-97G ELINT conversion of three KC-97Gs. 53-106 was operated by the Central Intelligence Agency for covert ELINT operations in the West Berlin Air Corridor. C-97G 135 KC-97Gs converted to transports. GKC-97G Five KC-97Gs were used as ground instruction airframes. JKC-97G One aircraft was modified to test the underwing General Electric J47-GE-23 jet engines, and was later designated KC-97L. HC-97G KC-97Gs converted for search and rescue operations, 22 converted. KC-97H One KC-97F was experimentally converted into a hose-and-drogue refueling aircraft. YC-97J two KC-97G conversion with four 4250 kW Pratt & Whitney YT34-P-5 turboprops, dropped in favour of the Boeing KC-135 Stratotanker. C-97K 27 KC-97Gs converted to troop transports. KC-97L 81 KC-97Gs modified with two J47 turbojet engines on underwing pylons. Operators Israel Defense Forces Spanish Air Force United States Air Force The following