Boeing Y1B-20

The Boeing Y1B-20 was a proposed experimental heavy bomber, an evolved and dimensionally larger offshoot of the Boeing XB-15 that carried the company designation Model 316. The XB-15 itself came from a 1933 United States Army Air Corps initiative for a bomber able to fly 5,000 miles at 200 miles per hour with a 2,000 pound bomb load. The Y1B-20 was designed around four Wright GR-2600-A73 radial piston engines of 1,350 horsepower each, which promised a maximum speed of 258 miles per hour (about 415 kilometres per hour), a cruising speed of 242 miles per hour and a range of 4,000 miles. It was to carry up to 17,600 pounds of bombs internally and to be defended by seven machine guns, three of .30 caliber and four of .50 caliber. Although the Army signed an order for two prototypes, the project was cancelled before work on either airframe began, so no example was ever completed. Like the XB-15 before it, it helped Boeing lay the foundation for the important bombers that served in the Second World War and after.