The first USN Depth Charge, introduced into service in February 1917. Commonly called an "ashcan," this was a relatively simple device. "There were no arrangements to launch them, and ships picked the strongest man in the crew to heave them over the stern when attacking a suspected periscope, oil slick, or unsuspecting whale." - from "Bayly's Navy." The DC divided into two sections when launched into the water; a float which remained on the surface and which unreeled a cable to the sinking explosive section. The explosive was triggered when the cable went taut. The depth could be easily set anywhere from 25 to 100 feet (6 to 30 m). The USN placed orders for 10,000 units, but this design proved too complicated for reliable action and the explosive charge was too small to be effective.

A note on sources: "US Naval Weapons" states that this DC weighed 200 lbs. (91 kg). However, based upon the photographs shown here and the description of how it was manually launched by a single sailor, it would seem that this is a misprint and the figure above the correct value.

In 1917 the USN rejected the British Thornycroft DC thrower as being over-engineered and too difficult to mass produced. At the same time, the USN was experimenting with the Davis non-recoiling AA gun. Lt. Cmdr. A.J. Stone, USNRF, proposed using this technique to launch depth charges. The result was the "Y" gun which fired two DC simultaneously, one to either side. Work began in 1917 at Stone's former employer, the General Ordnance Company in Groton, Connecticut, prior to receipt of a formal order on 8 December 1917. The first projector was delivered two days later. This became standard equipment during World War I on many destroyers and sub-chasers, with 974 being produced.

These projectors used a 3" (7.62 cm) blank cartridge to fire the arbors (depth charge holders). The arbors were inserted into each arm of the projector and then the depth charges were placed onto the arbors. After the gun was fired, the arbors fell into the sea separately from the depth charges. The charge could be varied to provide ranges of 50, 66 or 80 yards (46, 60 or 73 m).

The Y-gun projectors took up precious centerline space and could not be quickly reloaded following an attack. Destroyers carried at most two, but more usually one, projector. Marks 5 and 7 were modified versions of the Mark 1 and the Mark 8 was not in service.

Known as the "K-gun" as it resembled the letter "K", the Projector Mark 6 was introduced in 1941 just in time for World War II. Fired a single Mark 6, 9 or 14 depth charge to ranges of 60 to 150 yards (55 to 137 m) with a flight time of 3.4 to 5.1 seconds. Since the Mark 6 did not need to be sited on the centerline, many more could be used on each ship. Typically, four to six were mounted on destroyers while destroyer escorts carried eight. Still used up to the 1950s in the USN. A number of K-guns were supplied to Britain and other Allies as part of Lend-Lease. Arbors had a moveable stop whose position was changed when used with a British Depth Charge Mark 7 Heavy.

Like the Y-gun, this projector required an arbor (holder) which had to be inserted into the projector before the depth charge could be loaded and which fell into the sea separately from the depth charge. Arbors consisted of a tubular stem 24 inches long by 6 inches in diameter (61 cm x 15 cm), closed on one end and with a 12 by 31 inch (30.5 x 79 cm) tray welded to the open end. The stem fits into the projector barrel and acts as a projectile when fired. The arbor weights were: Mark 6, 70 lbs. (32 kg); Mark 7 and Mark 7 Mod 1, 65 lbs. (29.5 kg).

The propellant was black powder in a 3" (7.62 cm) casing and was supplied in three loads for ranges of 60, 90 and 150 yards (55, 82 and 137 m).

The Depth Charge Projector Mark 9 was a revised version of the K-gun with a built-in arbor that was tested in 1944 on the frigate USS Asheville (PF-1). The weight savings proved trivial and the project was abandoned.

First USN Hedgehog projectors, adapted from the British 24-spigot mortar. More popular and more successful with the USN than with the Royal Navy, possibly because of better sonar detection practices. Production in the USA began in late 1942 and differed from the British design in being both more rugged and more flexible in operation. A target designation transmitter and gun train indicator, both based upon the British models, provided a greater measure of control than was available with conventional depth charges.

Projectiles were 7.2 inches (18.3 cm) in diameter and weighed 65 lbs. (29.5 kg) with an explosive charge of 35 lbs. (15.9 kg) of Torpex. Sinking speed was 22 to 23.5 fps (6.7 to 7.2 mps). Mark 10 fired an elliptical pattern 195 feet (59 m) in width and 168 feet (51 m) long at a range of 283 yards (259 m). The Mark 11 fired a circular pattern 267 yards (244 m) wide at a range of 267 yards (244 m) from the firing ship. Could be trained up to 25 degrees by tilting the firing platform. Total weight for a dual installation and six reloads was 28,720 lbs. (13,027 kg).

Missiles were fired in pairs with an interval of either 0.1 or 0.2 seconds between pairs. The order was such that the missiles with the highest trajectories were fired first while those with the flattest trajectories were fired last. This allowed all missiles to hit the water at about the same time. Reload time was 3 minutes. When aimed to impact at 200 yards (180 m) from the firing ship, it took about 17 seconds from the time the missiles were fired until they sank to a depth of 200 feet (61 m) and 34 seconds to reach a depth of 600 feet (183 m).

Some of the advantages of this weapon were that:

1. They only exploded if they hit something, which meant that the firing ship could more quickly make follow-on attacks if the previous attack was unsuccessful.
2. Since unsuccessful attacks did not disturb the water, ASDIC/Sonar performance was not affected.
3. The projectiles had a higher sinking rate than conventional depth charges which again sped up the time that it took to make follow-on attacks.

The principle disadvantage of Hedgehog was its 40 ton recoil force, which precluded it being used on small warships. This led to the development of Mousetrap, as described below.

It should be noted that the USN considered that the Hedgehog projectiles to be missiles, not rockets, as the propelling charge was entirely used up prior to the projectile leaving the spigot. Propellant was NC in USN service.

Mousetrap rocket projector with four rails. This weapon was originally classified as a Rocket Launcher and retained its original Mark number when reclassified as an ASW projector. This weapon was developed to take the place of Hedgehog for smaller ships such as patrol craft which could not withstand the recoil forces generated by that weapon.

An 85 lbs. (39 kg) projectile was originally used, but this was too heavy to man-handle in rough seas. The warhead was changed to the lighter one of the Hedgehog (see above), which had the added benefit of simplifying logistics.

The mountings were usually fitted in pairs and could not be compensated for rolling. Launcher had a fixed elevation of 48 degrees. Not considered to be as effective as Hedgehog, but did give those smaller ships an ahead-firing weapon.

Projectiles were 7.2 inches (18.3 cm) in diameter and weighed 65 lbs. (29.5 kg) with an explosive charge of 31 lbs. (14.1 kg) of TNT. Torpex warheads added about 2.5 lbs. (1.1 kg) to the overall weight. Total length was 38.6 inches (98 cm). Unlike the Hedgehog missile projectiles, this projectile was classified by the USN as a rocket as it uses a sustainer propellant that burned for 0.2 to 0.7 seconds.

Originally known as Weapon Able, this was later known as Weapon Alfa or Alpha. The original Mark 108 launcher was based on the twin 40 mm Bofors gun mount and weighed 22,760 lbs. (10,324 kg). The later, purpose-built mounting had a weight of 25,240 lbs. (11,450 kg). Total weight of the latter mounting with 72 rounds was 85,000 lbs. (38,560 kg). Weapon Alfa could fire 12 rounds per minute and held 22 rounds in a ready-service ring. Train rate was 30 degrees per second, maximum elevation was 85 degrees. To reload, the launcher was elevated to 90 degrees and the rockets then loaded from below. Rockets entered the water at 1,300 fps (396 mps). Fuzing was magnetic influence type.

In 1963 these rockets were designated as RUR-4A Mark 1 and RUR-4A Mark 2.

Rocket Assisted Torpedo (RAT) was the first long-range, ship-launched ASW torpedo system to enter service in the USN. Installed in pairs on twin 5"/38 (12.7 cm) gun-houses, one on each side. There was to have been an alternative version for ships that did not have 5" (12.7 cm) gun-houses but this was dropped from development. Originally, each missile carried a Mark 43 Mod 4 acoustic-homing torpedo which had a maximum speed of 15 knots but this was later replaced with the Mark 43 Mod 3 which had a speed of 21 knots. Maximum range was 5,000 yards (4,572 m). The RAT launchers were installed only on USS De Haven (DD-727) and USS Sarsfield (DD-837). Each launcher could hold five missiles, one on the launch rail and four in an adjacent ready-use magazine. RAT was superseded by the longer ranged ASROC.