The 1.1-inch/75-caliber quadruple-mount antiaircraft gun — nicknamed the “Chicago Piano” for the way its four vertical barrels resembled organ pipes — was the US Navy’s standard close-in antiaircraft weapon in the years leading up to World War II. Faster-firing than the old .50-caliber machine guns it replaced, the quad 1.1 nonetheless earned a poor reputation in fleet service: the mount jammed frequently and its actual rate of fire fell well short of the design specification. By 1942 most ships were re-arming with the far more reliable 20mm Oerlikon and 40mm Bofors guns, and few examples of the 1.1-inch mount survive today. The photos below show a preserved quad 1.1 mount, its four barrels and open breech visible on static outdoor display.
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