Chase XCG - 20 The Chase XCG - 20 , also known as the XG - 20 and by the company designation MS - 8 Avitruc , was a large assault glider developed immediately after World War II by the Chase Aircraft Company for the United States Air Force , and was the largest glider ever built in the United States . The XG - 20 did not see production due to a change in USAF requirements , however , it was modified into the successful Fairchild C - 123 Provider twin - engined transport aircraft which saw extensive service in the Vietnam War . Design and development . Following the end of the Second World War , the United States Army Air Forces , which became the United States Air Force ( USAF ) in 1948 , developed a requirement for a new , large assault glider type to replace smaller types that were then in service , all existing gliders having been declared obsolete . The new gliders were to be constructed entirely of metal , and were also required to be easily adaptable to a powered configuration . As part of a five - year development program , a contract was awarded to the Chase Aircraft Company of Trenton , New Jersey , in August 1946 for the construction of two types of gliders . These included a smaller model being designated XCG - 18A , and the larger , definitive model being designated XCG - 20 . The XCG - 20 , redesignated XG - 20 in 1948 with the establishment of the USAF , was the largest glider ever constructed in the United States , and the last combat glider to be built for the United States military . It featured a high - mounted wing and retractable tricycle landing gear , with an auxiliary power unit supplied hydraulic power to the landing gear and flaps . The nose section was reinforced to provide optimal protection to the pilots in the event of a crash on landing , and to allow for the strongest possible towing connection . The cargo hold was long and wide ; it featured an innovative configuration , the rear fuselage being upswept with an integrated loading ramp . This allowed vehicles to be driven directly on and off of the aircraft , speeding loading and unloading times . Operational history . Although the first prototype XG - 20 never flew as a glider , the second prototype conducted the aircraft ' s first flight in April 1950 . Following being displayed to the public at Pope Air Force Base as part of Exercise Swarmer during that month , the XG - 20 underwent thorough flight testing ; during the late summer , it was evaluated against a variety of other transport aircraft at Eglin Air Force Base in Florida . Although it possessed no obvious faults , the test program confirmed that the powered " assault transport " was the equal of the glider in landing performance ; having been rendered obsolete , the assault glider fell out of favor with the Air Force , and the XG - 20 project was cancelled . However , Chase had designed the aircraft to allow for the easy installation of engines ; the first XG - 20 had already been modified with two radial piston engines , becoming the XC - 123 , the prototype of the long - serving C - 123 Provider family of transports . Meanwhile , the second prototype XG - 20 was returned to Chase Aircraft , to be fitted with two twin pods for General Electric J47 turbojets , becoming the XC - 123A , the first jet - powered transport aircraft built in the United States .