This aircraft was bailed from the USAF to Lockheed for use in Operation Hourglass, as part of the Electra program. Although the Allison 501D engine was proving reliable, Lockheed flew the aircraft for 30 days on a carefully planned 'airline' schedule in order to test its durability for commercial operations, which involved much longer operational days and multiple daily flight cycles, than the engine had thus far experienced in military use. Photo from Lockheed Aircraft Corp.