Only a few old hands probably recognize the odd-looking U.S. Navy shipboard antiaircraft gun often seen in action in World War II movies and television features. The four-barrel 1.1- inch mount usually seen blazing away at attacking Japanese aircraft was known in its time as the “Chicago Piano.”
It was developed as a result of the early 1920s joint services air attack tests against warships, which led the Navy to issue requirements for shipboard antiaircraft defense systems. Until then, the Navy had relied exclusively on an assortment of small-caliber machine guns and three-inch dual purpose guns.
By the mid-1920s, the first of the dual- purpose five-inch guns were being mounted on warships; by the end of the decade, Browning water-cooled .50-caliber antiaircraft machine guns also were being fitted.
The Navy wanted another automatic antiaircraft gun, however, to fill the range and effectiveness gap between the machine guns and the larger dual-purpose guns. The planners wanted a high-velocity automatic gun, firing a super-sensitive high-explosive shell weighing about one pound, but the Navy was unable to find such a weapon at the time.
About 1930, Robert F. Hudson, a Richmond, Virginia, inventor, offered the Navy a series of new automatic guns that promised to meet the one-pound shell automatic gun requirement. He had begun developing them during World War I to provide an aircraft gun that could fire high- velocity ammunition with minimum recoil.
The Hudson Gun had an unusual operating system that was described in his series of patents dating from 1920 to 1938; the guns used a complicated gas- recoil operating system described as “gas-set, spring operated.” By 1930, Hudson had a series of prototype guns that fired .30-caliber rifle ammunition, .50-caliber machine gun ammunition, and a special new 1.1-inch high- velocity round. The 1.1-inch interested the Navy because it filled the requirement it had for an intermediate-caliber automatic gun.
The 1.1-inch Hudson was the only one of its type seriously considered by the U.S. Navy at the time. The Navy tested a water-cooled prototype at the Dahlgren Proving Grounds, Dahlgren, Virginia, in 1933, and reported that its “entire performance . . . [was] satisfactory.” As a result of the sucessful trials, the Navy decided to develop the gun and mounts. In 1934, the U.S. Naval Gun Factory, Washington, D.C., began work on the project, a 1.1-inch Hudson that was water-cooled for sustained fire. It could fire 150 one- pound high explosive shells per minute with a muzzle velocity of 2,700 feet per second to a maximum range of 7,000 yards.
The Navy decided to mount the guns in groups of four to achieve roughly the same rate of fire and resulting projectile density of existing water-cooled Browning .50-caliber antiaircraft machine guns. The design of the 1.1 Quadruple mount, normally referred to as a Quad-mount, included some unusual features. It was capable of elevating to 110°—past the vertical—instead of the 85° capabilities used on practically all other antiaircraft mounts. The mount also had a sub-traverse mechanism that enabled the gunner to make rapid fine adjustments in aim. Initially manually traversed and elevated, the mount was later power-driven.
The prototype 1.1-inch Quad mount system was tested in 1935, and the guns and mount were full of bugs. Most serious, the mount vibrated badly because it was not rigid enough. Possibly as a result of this, the guns tended to jam, and clearing the super-sensitive fused ammunition was an unpleasant job.
Improvements and modifications were made, more testing done, and by 1938, the 1.1-inch Quad mount was ready for production at the Naval Gun Factory. The first system went aboard ship in 1939 and was quickly nicknamed “The Chicago Piano for the way it was fired,” a name that stuck as long as it was in service.
By 1941, the 1.1-inch Quad mount had been mounted on everything from destroyers to battleships and carriers, and even on a few battle fleet support ships.
The 1.1 Quad first saw action during the Japanese attack on Pearl Harbor, 7 December 1941. Although a large amount of 1.1-inch ammunition was expended, unfortunately there are no records of what, if anything, it hit. There are records, however, of 1.1-inch shells which did not have the self-destruct provisions landing on shore and exploding like hand grenades.
Soon after the Pearl Harbor attack, however, the U.S. Navy began to improve its shipboard light antiaircraft firepower. The 20-mm Oerlikon automatic guns were replacing the .50-caliber machine guns, and the 40-mm Bofors—in single, twin, and quad mounts—began to replace the 1.1- inch Quad mount.
Some 1,000 Quads were built before production eneded in 1942, and although the 1.1 Quads on many ships were replaced by 1943, they remained on many older ships and auxiliaries until the end of the war in 1945, albeit in ever decreasing numbers.
During the war, crews complained that its complex mechanism was very difficult to maintain in operation. It required much work and tinkering by a highly skilled crew to keep it in service, although when it was working properly it was effective. One problem the 1.1 Quad never overcame was its overall weight—five to six tons each. The twin water-cooled 40-mm. Bofors weighed about the same and the water- cooled quad 40-mm Bofors weighed about twice as much—but the Bofors was a much more powerful gun.
The 20-mm Oerlikon mounts, which some authorities considered as effective as the 1.1 Quads, weighed about 1,500 pounds. The air-cooled Oerlikon’s rate of fire was about twice that of a 1.1-inch Quad, but the water-cooled Quad could maintain better sustained fire. The Oerlikon’s weight advantage, however, meant that at least a half-dozen air-cooled Oerlikons could be mounted as opposed to a single Quad for the same weight—a real consideration in fighting the aggressive Japanese air attacks.
Soon after the end of World War II, the Navy scrapped the 1.1 Quads, along with the older ships that carried them. Such a thorough job of scrapping was done that few survive today, and these are all either in museums or on preserved historic warships.