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Davis anti-submarine gun. World War I-era anti-submarine gun mounted on a flying boat. The Davis gun was developed in 1910 by Cleland Davis of the US Navy. It was the first successful recoilless gun, with the recoil from the downward projectile cancelled out by the recoil from a counter-projectile that travelled out of the rear barrel and over the wing of the aeroplane. The Lewis machine gun mounted on the Davis gun was used for sighting. The Davis gun was intended for use against submarines. Photographed in November 1918. (KEYSTONE/SCIENCE PHOTO LIBRARY/LIBRARY OF CONGRESS/SCIENCE PHOTO LIBRARY)