This is a practice round of a 4.5-inch caliber U.S. air-to-surface rocket used during World War II. The rocket, developed from 1940, could also be used as a ground-to-ground weapon. When used from aircraft, like the P-40, it had five folding fins and was launched from tube launchers under each aircraft wing. The rocket's first operational use came in late 1943 or early 1944 against Japanese ground installations in Burma - the first combat use of American aircraft rockets. The range of the 4.5-in. rocket was about 1-2 miles. The payload weighed 4.3-5 pounds depending on the type of high explosive in the warhead. This rocket was donated by the U.S. Army Ordnance Museum to the Smithsonian in 1989.