To add firepower to the list, the Navy sought a lightweight aircraft weapon that could respond immediately to a target sighting—a gun, in other words. Even in the earliest days of World War I, as aircraft first proved themselves viable combat platforms, designers attempted to fix artillery-caliber weaponry onto aircraft. Guns would have to be of large calibers, and thus heavy, to be effective against submarines, but the wood, wire, and fabric structures of the planes of the era were not substantial enough to absorb the recoil of a heavy weapon undamaged.
Fortunately, the Navy had on hand an officer who had developed a solution.
In 1910, Commander Cleland Davis began experimenting with a “non-recoil” gun, an “apparatus for firing projectiles from aeroplanes,” for which he received Patents No. 1,108,715 and 1,108,716 in 1914. The invention was deceptively simple. It consisted of two barrels attached inline at the center to a common chamber, the breech. The forward-pointing barrel contained the projectile, while the aft-pointing barrel contained a “counter shot” with a mass equal to that of the projectile. The weapon’s powder charge was placed in the central chamber and fired. As the projecticles moved down their respective barrels with equal acceleration, the recoil from each canceled the other, resulting in the first workable recoilless gun to be accepted into military service.
The weapon’s most obvious disadvantage was the requirement for a safe area behind the gun for the counter shot, because it was a projectile. Improvements attempted to reduce the lethality of the counter shot by replacing it with an equivalent mass of lead pellets packed in grease—buckshot, essentially. A further refinement eliminated the counter shot entirely, instead expelling the heavy steel cartridge case to the rear, which also left the breech clear for the next round.
The Davis recoilless gun underwent initial tests at Naval Proving Ground Indian Head in Maryland on 3 October 1912 and again in early December. The experiments demonstrated that although the gun was recoilless, its muzzle blast was a hazard when installed on airplanes. But aircraft design was evolving quickly, and within two years, structures had become substantial enough to support the weapon.
The gun was produced in multiple sizes: the 1.57-inch-diameter 2-pounder, the 2.45-inch 6-pounder (also called the Mark 12), the 3-inch 12-pounder (also called the Mark 15), and a Mark 13 9-pounder, which was a bored-out Mark 12. The Mark 15, 24-caliber system weighed 182 pounds (not counting the breech block) and fired with a chamber pressure of 30,000 pounds per square inch. The Davis Gun system also usually mounted a Lewis machine gun on top of the barrel for sighting and antiaircraft protection.
The British showed early interest in the Davis Gun, testing a 6-pounder at Shoeburyness just before the war. Its smooth bore rendered it extremely inaccurate, but rifling the projectile barrel rectified this. Further tests from December 1917 to June 1918 attempted to determine the best type of projectile to use against a shallow submerged submarine. Three Royal Aircraft Factory F.E.2h airplanes were modified to carry a Davis Gun for testing, but the conditions required for the gun to be effective were found far more limiting than those for a standard bomb. Further, the gun was deemed heavy and clumsy with its aft-facing safety zone, and it limited its aircraft’s bomb load. The Royal Flying Corps modified at least one Handley Page O/100 bomber to mount one Davis Gun for use against Zeppelins.
On 26 August 1918, U.S. Vice Admiral William S. Sims recommended to the Office of the Chief of Naval Operations that the Davis Gun be given a thorough trial in the United States before being adopted and installed on seaplanes in the war zone. The gun was mounted on some Curtiss HS-2L and H-16 flying boats, but the extent of their testing and employment is not well documented.
The naval air arms of both the United States and Great Britain designed airplanes specifically to carry Davis Guns, and both suffered similar fates. The Robey-Peters Gun-Carrier was an unusual three-seat tractor biplane designed and built by Robey & Company Limited at Bracebridge Heath, Lincoln, for the Royal Naval Air Service (RNAS). This was a single-engine, three-bay biplane powered by a 250-hp Rolls-Royce Eagle engine. The aircraft had two gondolas—each carrying a 2-pounder Davis Gun and a gunner—attached to the upper wings. The pilot sat in a cockpit in the rear fuselage, which was suspended between the two wings, just forward of the tail. Two were ordered for the RNAS in May 1916, but the first crashed on its maiden flight in May 1917. In the end, the Royal Navy passed on the Davis Gun. The second aircraft was not completed, and no others were built.
The U.S. Davis Gun Carrier, later designated N-1, was as unusual as the British airplane and was the first purpose-built Navy attack aircraft. Like the Robey-Peters plane, the float-mounted N-1 biplane carried its short bathtub-like fuselage, which accomodated a two-man crew, between its wings, ending just behind the wing in a 330-hp Liberty engine and pusher propeller. Its sole weapon was a nose-mounted 2-pounder Davis Gun. The biplane tail, attached by a latticework frame, was supported by a float. Three aircraft were ordered, BuNo. A-2282 to A-2284, but the third was canceled. The first aircraft was completed on 22 May 1918 but was damaged in an accident before flying. The second aircraft first flew on 27 July 1918. Two later N-1s were built, BuNo. A-4341 and A-4342, but an additional ten, BuNo. A-5030 to A-5039, were canceled.
During its lifetime, the aircraft-mounted Davis Gun was little known even in the services that used it, with only a few photographs and scant records available. The guns were also mounted on World War I–era sub chasers; at least 25 boats were so equipped. In June 1918, the Office of the Chief of Naval Operations recommended that Poole 3-inch, 23-caliber guns replace Davis Guns on smaller craft, and it added the Poole gun to troop transports and freighters as well. In all, the General Ordnance Company produced 149 Davis Guns in 1917. Before the gun faded into complete obscurity, Davis promoted its use in 1920 for an antiship aircraft that was to have carried as many as 30 12-pounders. Drawings exist, but it was never built.
The service of the Davis Gun, however, is not over. Sandia National Laboratories uses 8-, 12-, and 16-inch bore Davis Guns for weapon testing. As recently as May 2015, the 40-foot-long 16-inch gun was used for impact testing of hardware in the nose assembly of a mock B61-12 nuclear bomb, part of the bomb’s decade-long service life extension program.