Weapon of War: The Y-Gun Depth Charge Launcher

A Chief About to Launch Two Depth Charges

Although the British basically invented the depth charge—which was the most effective anti-submarine weapon—the U.S. Navy contributed significantly by improving the hydrostatic detonator, developing the depth charge rack (enabling depth charges to be rolled off the stern, instead of craned off in a net) and developing the “Y-gun,” enabling smaller depth charges to be fired abeam and ahead of the ship—reducing the target U-boat’s chance of escape. 

Y-guns were developed by the U.S. Navy's Bureau of Ordnance from the British single-launch Thornycroft thrower and became available in 1918. Mounted on the center-line of the ship with the arms of the Y pointing outboard, two depth charges were cradled on shuttles inserted into each arm. An explosive propellant charge was detonated in the vertical column of the Y-gun to propel a depth charge about 45 yd (41 m)  over each side of the ship. The main disadvantage of the Y-gun was that it had to be mounted on the center-line of a ship's deck, which could otherwise be occupied by superstructure, masts, or guns. The first were built by New London Ship and Engine Company beginning on 24 November 1917.

The Double Launch Leaves the Ship

The lighter, more easily loaded, single-action K-gun, standardized by the U.S. Navy in 1942, replaced the Y-gun as the primary depth charge projector for the Second World War.

Sources:  U.S. Navy; Wikipedia