Martin XB-16

The Martin XB-16, company designation Model 145, was a projected heavy bomber that the Glenn L. Martin Company designed in the 1930s for the United States Army Air Corps, which wanted an aircraft able to carry 2,500 pounds of bombs over 5,000 miles. Martin proposed four liquid-cooled Allison V-1710 engines, unusual at a time when American aircraft used air-cooled radials, and in 1935 reworked the layout as the larger Model 145B, whose wingspan was 20 percent greater than that of the later B-29 Superfortress. The Army judged it not fast enough, as it had the Boeing XB-15, and the project was cancelled before any airframe was built, so it survives only as a design study.