The Davis gun mounted on a Curtiss flying boat
The contraption was not a recoilless gun as much as two guns connected back-to-back, with one firing a round in the direction of the enemy and the other one firing a mass of lead balls and grease to counteract the recoil. Although the counterweight was designed to disperse upon firing, it obviously had to be pointed in a safe direction, The counterweight was typically lobbed rearward and over the top wing of the aircraft. The first Davis guns were smoothbores, but subsequent models were rifled to improve accuracy.
1914 patent for Davis gun Shell.
Experiments were conducted by the British Royal Naval Air Service (RNAS), the Royal Air Force (RAF) and the American Air Service. The Davis gun was supposed to be used against, for example, Zeppelins and U-boats. It was mounted on Handley Page O/100 and F.E.2b bombers, as well as on Curtiss HS-2L and H-16 flying boats after unsuccessful attempts to use N-1 and N-2 flying boats. Other experimental aircraft were also used.
In 1915, a Haris Booth at the Admiralty Air Department designed the A.D. Scout, a “lofty, but quite unsuitable” aircraft with a nacelle some ten feet over the ground carrying the upper wings. It was to have mounted the Davis gun for use against Zeppelins, but the development was not completed. The Davis gun was also thought of for the Blackburn Triplane, the P.V.2 seaplane and the Robey-Peters three-seat gun carrier, although these projects remained on the drawing board.
The A.D. Scout or "Swallow"
The RNAS and subsequently the RAF did conduct a series of trials with F.E.2B aircraft between December 1917 and June of 1918 to determine the best type of projectile to be used against a shallow submerged U-boat. It was found that the gun had to be fired from very low altitude and almost vertically to have a 12-pund shell penetrate a U-boat at a depth of 25 feet. The gun was thus deemed to be more suitable for use against surfaced submarines. In the end it was decided that the Davis gun was too heavy for practical use, and that bombs or 37mm conventional guns were preferred for use against u-boats. The Davis gun was also briefly mounted on US Navy subchasers.
The Davis gun was declared obsolete at the end of the First World War.
Norman Friedman. Naval Weapons of World War One
David P. Williams. Night Fighters: Hunters of the Reich