In February 1921, at the urging of Billy Mitchell, who was anxious to test his theories of destruction of ships by aerial bombing, Secretary of War Newton Baker and Secretary of the Navy Josephus Daniels agreed to a series of joint Army-Navy exercises, known as Project B, to be held that summer in which surplus or captured ships could be used as targets.
On July 20, 1921, the Navy brought out the ex-German World War I battleship, Ostfriesland. On the scheduled day, 230, 550, and 600 lb (270 kg) bomb attacks by Navy, Marine Corps, and Army aircraft settled the Ostfriesland three feet by the stern with a five-degree list to port. She was taking on water. Further bombing was delayed a day, the Navy claiming due to rough seas that prevented their Board of Observers from going aboard, the Air Service countering that as the Army bombers approached, they were ordered not to attack. Mitchell's bombers were forced to circle for 47 minutes, as a result of which they dropped only half their bombs, and none of their large bombs
The fact of battleship sinking was indisputable, and Mitchell repeated the performance twice in tests conducted with like results on the U.S. pre-dreadnought battleship USS Alabama in September 1921, and the battleships USS Virginia and USS New Jersey in September 1923. The latter two ships were subjected to teargas attacks and hit with specially designed 4,300 lb (2,000 kg) demolition bombs.

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