The Aero Spacelines B-377PG Pregnant Guppy was flown to Dryden for tests and evaluation by pilots Joe Vensel and Stan Butchart in October 1962. The outsized cargo aircraft incorporated the wings, engines, lower fuselage and tail from a Boeing 377 Stratocruiser with a huge upper fuselage more than 20 feet in diameter. The modified aircraft was built to transport outsized cargo for NASA's Apollo program, primarily to carry portions of the Saturn 5 rockets from the manufacturer to Cape Canaveral.

Later versions of the aircraft, included the Super Guppy and the Super Guppy Turbine. The fourth and last Super Guppy Turbine, built in 1979-80 for Airbus Industrie, was obtained by NASA Johnson Space Center from the European Space Agency in late 1997 to ferry outsize components of the International Space Station from their manufacturers around the world to launch sites in preparation for sending them into orbit. It is the last of the Guppy aircraft still flying.