Presumably inspired by the German "Paris Gun" of World War I, this experimental weapon was converted from a 14"/50 (35.6 cm) gun by lengthening it with a hoop of alloy steel to 900 inches (22.860 m) and installing a heavy alloy-steel liner. The chamber volume was equivalent to that used for the 14" (35.6 cm) guns and the rifling was to be increasing RH from 1 in 48 to 1 in 45. Weight with breech block was 209,429 lbs. (94,996 kg). This weapon was designed to fire a 275 lbs. (125 kg) projectile at a muzzle velocity of 5,000 fps (1,524 mps). The gun was almost completely finished except for the rifling when the project was cancelled about 1919.
A reduced-scale version of this weapon was the 3"/105 (7.62 cm) Mark 16.