Lockheed XC-35 Electra

In 1935, the U.S. Army Air Corps established requirements for a pressurized cabin airplane. This aircraft was intended as an experimental flying laboratory to test new equipment and engineering practices involved in high altitude flying. In June 1936, the War Department contracted with Lockheed Aircraft Corporation for the delivery of the "XC-35 Supercharged Cabin Transport Airplane, (plus) Mock Up and Data Applicable Thereto" at a cost of $112,197. This airplane would be capable of flying at an altitude of no less than 7,620 m (25,000 ft) for ten hours with at least two hours of continuous flight at that altitude or higher.

After flight-testing at Lockheed's Burbank, California, plant, the XC-35 was delivered to the Army Air Corps at Wright Field, Dayton, Ohio, where Air Corps pilots began extensive evaluation of the airplane's systems and capabilities. The XC-35 demonstrated its outstanding capabilities on one test flight when it attained a maximum speed of 560 kph (350 mph) (with the benefit of a tailwind) over a 352 km- (220-mi) course while maintaining an average altitude of 6,096 m (20,000 ft). Contemporary news articles reported that "neither oxygen equipment nor heavy clothing was necessary at the highest altitude." The U.S. Army Air Corps was awarded the Collier Trophy in 1937 for sponsoring and developing the XC-35.

The Lockheed XC-35, with commercial serial number 3105 and military serial number 36-353, was donated to the Smithsonian Institution in 1948.