Mark 108 anti-submarine rocket launcher tested on the submerged U-2513 on October 7th 1951

The RUR-4 "Weapon Alpha" (originally Weapon Able) was an American naval ahead-throwing anti-submarine warfare (ASW) rocket launcher. It was designed between 1946 and 1949, and was installed on warships from 1951 to 1969. Unlike depth charges, it was designed to attack enemy submarines without requiring the attacking ship to be located directly above the submarine being attacked.

Weapon Alpha was developed toward the end of World War II, in response to the German Type XXI U-boat. Begun in a crash program in 1944-5 and put in service before undergoing operational evaluation, it emerged in 1949 as a 113 kg (250 lb) warhead propelled by a 5 inch rocket that sank at 12 m/s (40 ft/s) (compared to a depth charge, which sank at 2.7–5 m/s (8.9–16.5 ft/s)), an influence or time pistol, and a range of 360–730 m (400–800 yd). Coupled to the new SQG-1 depth-finding sonar (for setting the time fuze, rather than the hydrostatic pistol of a depth charge), it was to be fired from a revolving Mark 108 launcher (with 22 rounds of ready ammunition) at up to twelve rounds per minute.

In this footage the Mark 108 launcher is seen mounted on the destroyer USS Robert A. Owens during trails that culminated in the targeting of the German submarine U-2513, a Type XXI U-boat formerly operated by the Kriegsmarine. She had been commissioned on October 12th 1944 with Kapitänleutnant Hans Bungards in command. Bungards was relieved on April 27th 1945 by Fregattenkapitän Erich Topp, who commanded the boat for less than two weeks.

U-2513 conducted no war patrols. On 8 May 1945, Topp surrendered his command at Horten Naval Base, Norway. U-2513 was taken to Oslo on 20 May, then to Lishally, Northern Ireland, which she reached on 7 June. In August 1945, the U-boat was transferred to the United States. After an extensive evaluation she was sunk as a target about 23 miles northwest of the Dry Tortugas (70 miles west of Key West) in about 65 m of water at 24°52.015′N 83°18.594′WCoordinates: 24°52.015′N 83°18.594′W.

0:00 Test firing of the Mark 108 launcher on USS Robert A. Owens using inert rounds
0:16 Test firing of inert rounds seen from the bridge, note how the tube returns to the vertical position for reloading
0:41 U-2513 prepared for its final voyage
0:50 Test firing of inert rounds at the submerged submarine for ranging purposes
1:19 Impact of the first live round on the submarine hull
1:34 Impact of the second live round with a smaller surface splash after the submarine hull had already been compromised by the first round
1:56 Artist's impression of the damage to the submarine based on a diving survey