Question: The Boeing 377 Stratocruiser was a large long-range airliner developed from the C-97 Stratofreighter military transport, itself a derivative of which four-engine propeller-driven heavy bomber designed by Boeing, which was flown primarily by the United States during World War II and the Korean War?
Context: "Kampfgeschwader" 40 (KG 40) was a Luftwaffe medium and heavy bomber wing of World War II, and the primary maritime patrol unit of any size within the World War II Luftwaffe.  It is best remembered as the unit operating a majority of the four-engine Focke-Wulf Fw 200 "Condor" maritime patrol bombers.  The unit suffered from the poor serviceability and low production rates of the Fw 200 bombers, and from repeated diversion of its long-haul capability aircraft to undertake transport duties in various theatres, especially for the airlift operations to supply encircled forces in the Battle of Stalingrad.  Later in the war, KG 40 became one of several Luftwaffe bomber wings to use the Heinkel He 177A heavy bomber. The Heinkel He 277 was a four-engine, long-range heavy bomber design, originating as a derivative of the He 177, intended for production and use by the German Luftwaffe during World War II.  The main difference was in engine configuration.  Rather than using two fire-prone Daimler-Benz DB 606 "power system" engines, each of which consisted of side-by-side paired Daimler-Benz DB 601s and with each DB 606 "power system" weighing 1.5 tonnes apiece — or two of the similar DB 610, each of which used a pair of DB 605 engines in a similar "twinned" configuration on later He 177A airframes (the A-3 model and onwards), the He 277 was meant from the outset to use four BMW 801E 14-cylinder radial engines, each mounted in an individual nacelle and each turning a three-blade, four-meter diameter propeller.  The design was never produced, and not a single prototype airframe was ever completed, owing both to the deteriorating condition of the German aviation industry late in the war, and the competition from other long-range bomber designs from other firms, competing for Germany's increasingly scarce aviation production capacity.  Although not specifically intended for it at first, partially due to the time-frame in the spring of 1942 in which its ultimate niche was requested for by the RLM, the He 277 design essentially became Heinkel's entry in the important trans-oceanic range "Amerika Bomber" competition, struggling to compete against both several other designs from rival firms in the competition for a truly trans-oceanic ranged bomber for the Luftwaffe, and Germany's own rapidly degrading ability, from Allied bombing damage to its aviation plants, to produce military aircraft of any sort. The Boeing 377 Stratocruiser was a large long-range airliner developed from the C-97 Stratofreighter military transport, itself a derivative of the B-29 Superfortress.  The Stratocruiser's first flight was on July 8, 1947.  Its design was advanced for its day; its innovative features included two passenger decks and a pressurized cabin, a relatively new feature on transport aircraft.  It could carry up to 100 passengers on the main deck plus 14 in the lower deck lounge; typical seating was for 63 or 84 passengers or 28 berthed and five seated passengers. The Boeing B-29 Superfortress is a four-engine propeller-driven heavy bomber designed by Boeing, which was flown primarily by the United States during World War II and the Korean War.  It was one of the largest aircraft operational during World War II and featured state of the art technology.  Including design and production, it was the single most expensive weapons project undertaken by the United States in World War II, exceeding the cost of the Manhattan Project by between $1 and 1.7 billion.  Innovations introduced included a pressurized cabin, dual-wheeled, tricycle landing gear, and an analog computer-controlled fire-control system that directed four remote machine gun turrets that could be operated by a single gunner and a fire-control officer.  A manned tail gun installation was semi-remote.  The name "Superfortress" continued the pattern Boeing started with its well-known predecessor, the B-17 Flying Fortress.  Designed for the high-altitude strategic bomber role, the B-29 also excelled in low-altitude nighttime incendiary bombing missions.  One of the B-29's final roles during World War II was carrying out the atomic bomb attacks on Hiroshima and Nagasaki. The Boeing C-97 Stratofreighter is a long-range heavy military cargo aircraft developed from the B-29 and B-50 bombers.  Design work began in 1942, with the prototype's first flight being on 9 November 1944, and the first production aircraft entered service in 1947.  Between 1947 and 1958, 888 C-97s in several versions were built, 811 being KC-97 tankers.  C-97s served in the Berlin Airlift, the Korean War, and the Vietnam War.  Some aircraft served as flying command posts for the Strategic Air Command, while others were modified for use in Aerospace Rescue and Recovery Squadrons (ARRS). The Boeing B-17 Flying Fortress is a four-engine heavy bomber aircraft primarily employed by the United States Army Air Forces (USAAF) during World War II.  Developed by Boeing, a total of 12,731 aircraft had been produced by Boeing, Douglas and Lockheed from 1936 until 1945.  Over 8,000 were lost in either combat operations or training accidents.  The remaining combat veterans and early production models were stored and later scrapped in the vast scrap drives of the late 1940s, many going to aircraft boneyards like Davis-Monthan Air Force Base in Tucson, Arizona, the largest of its kind within the United States' borders. The Heinkel He 177 "Greif" ("griffin") was a large long-range heavy bomber flown by the Luftwaffe during World War II.  In general terms, the He 177 had payload/range capability similar to strategic bombers in the USAAF and RAF, although it had much higher figures for its cruising and maximum speeds. The Tupolev TB-3 (Russian: Тяжёлый Бомбардировщик , Tyazholy Bombardirovschik, Heavy Bomber, civilian designation ANT-6) was a heavy bomber aircraft which was deployed by the Soviet Air Force in the 1930s and during World War II.  It was the world's first cantilever wing four-engine heavy bomber.  Despite obsolescence and being officially withdrawn from service in 1939, the TB-3 performed bomber and transport duties throughout much of World War II.  The TB-3 also saw combat as a Zveno project fighter mothership and as a light tank transport. The Petlyakov Pe-8 was a Soviet heavy bomber designed before World War II, and the only four-engine bomber the USSR built during the war.  Produced in limited numbers, it was used to bomb Berlin in August 1941.  It was also used for so-called "morale raids" designed to raise the spirit of the Soviet people by exposing Axis vulnerabilities.  Its primary mission, however, was to attack German airfields, rail yards and other rear-area facilities at night, although one was used to fly the People's Commissar of Foreign Affairs (Foreign Minister) Vyacheslav Molotov from Moscow to the United States in 1942. The Bomber Mafia were a close-knit group of American military men who believed that long-range heavy bomber aircraft in large numbers were able to win a war.  The derogatory term 'Bomber Mafia' was used before and after World War II by those in the military who did not share their belief, and who were frustrated by the insistence of the men that the heavy bomber should take a primary position in planning and funding.
Answer: Boeing B-29 Superfortress