Boeing C-97A Stratofreighter of the Military Air Transport Service, USAF. The Boeing 377, also called the Stratocruiser, was a large long range airliner which was built after World War II. It was developed from the C-97 Stratofreighter, a military derivative of the B-29 Superfortress used for troop transport. The Stratocruiser's first flight was on July 8, 47 Released in the late-1940s, the aircraft was powered by four piston engines, driving tractor propellers. The aircraft had surprisingly low fuel consumption for the era and was able to cruise at about 32,000 feet. It also had a pressurized cabin, which was a relatively new feature to transport aircraft at the time. At cruising altitude the cabin altitude was 5,500 ft 1,700 m). Airlines were able to make transoceanic flights easier and faster with the new aircraft, which enabled easier international travel. The aircraft often made transoceanic flights to places like Hawaii that were much harder to get to before it. Nevertheless, they did not have great reliability (chiefly due to chronic problems with the extremely complex 28-cylinder R-4360 engines and the associated propellers), and only 56 were built for airlines The aircraft also had two decks. The upper deck was for economy class customers, while the lower was a VIP lounge and bar. Passengers could walk down and get a drink on the long flights, once the plane leveled off at cruising altitude. Most Stratocruisers had economy seats on both decks. When jet airliners were introduced in the late 1950s, propeller planes such as the Stratocruiser became uncompetitive for major airlines, and many were sold off to feeder lines. Others scrapped, while some were converted by Aero Spacelines to Guppys, which were versions of the Stratocruiser with an enlarged fuselage and turboprops. One version, the Super Guppy, was used by Airbus to transport aircraft parts between factories, since replaced with Airbus Belugas.