World War II Database

Country of Origin	United States
Type	Torpedo
Diameter	530.000 mm
Length	6.200 mm
Weight	1430.000 kg
Range	3.700 km
Machinery	Westinghouse Electric motor
Explosive Charge	272kg Torpex
Speed	54.00 km/h

Contributor: David Stubblebine

ww2dbaseThe first electrically driven torpedo used in combat by United States submarines was officially designated as the Mark XVIII but later became more universally denoted as the Mark 18. Previous torpedoes were powered by compressed air or, more commonly, a small wet-heater type of steam drive contained within the torpedo body, both of which created a very conspicuous trail of white foam behind the torpedo pointing directly back to the submarine. Besides leaving no wake, electric torpedoes could be launched by "swimming" directly out of their tubes without the need of a large compressed air bubble that could also give away the submarine's position. While electric torpedoes may have been less visible during their run, they also ran at considerably lower speeds compared to conventional torpedoes (29 knots vs. 46 knots) and they involved a host of technical matters requiring perpetual maintenance.

German submarines had been using electric Model G7e torpedoes in the Atlantic since 1936 and the British were able to recover a few of them after they ran up on the shore. These discoveries caused both the United Kingdom and the United States to accelerate development of electric torpedoes. In the United States, inter-war efforts created the Mark 20 electric torpedo in 1941, but it never went into production despite nearly twenty years of development. In early 1942, Chief of Naval Operations Admiral Ernest King urged the Navy's Bureau of Ordnance (BuOrd) to finalize the development of an electric torpedo. BuOrd directed the Naval Torpedo Station (NTS) at Newport, Rhode Island to work out the remaining problems with the Mark 20 or abandon the effort in favor of copying the German design. Unfortunately, these orders arrived just as the Navy's unrelated Torpedo Scandal of 1942 was blossoming.

Central to the Torpedo Scandal that surrounded the Mark 14 was the provincial and reticent nature of the Naval Torpedo Station at Newport, something that manifested itself mainly in painfully slow results. NTS continued working with General Electric on refining the Mark 20 while BuOrd worked separately with Westinghouse on a copy of the German G7e, designated the Mark 18. The direction from Admiral King had emphasized getting a workable model into service quickly. It was Westinghouse, building on both the work of the Germans and the work at NTS, that emerged first with a suitable design after just over five weeks of development. On 2 May 1942, the Navy contracted for 2,000 Mark 18 torpedoes.

Technical problems slowed delivery, however. Batteries built by subcontractors emitted too much hydrogen gas and the fine-machining of the component parts progressed slowly. Prototype testing also revealed problems. True to form, the Naval Torpedo Station at Newport contributed to the delays by offering absolutely no technical assistance to the BuOrd team finalizing the Mark 18. An officer on one of the submarines testing the Mark 18 described the obstructive attitude at NTS as akin to sabotage. Complaints from the submarine commanders went up through the operational chain of command to the highest levels, and then over to the highest levels of the administrative chain of command, before coming down to both development teams with terse orders to get along and get it done.

The first operational Mark 18 torpedoes, though still not perfected, went into service in Sep 1943. By this time, the improvements to the Mark 14's depth control and exploders brought about by the Torpedo Scandal translated directly to the Mark 18, so the remaining issues were confined only to the bugs in the propulsion system. The batteries were affected by water temperatures and the torpedoes required frequent removal from their tubes to be recharged. Many of the weapon's maintenance procedures were new and arduous, particularly in the confined spaces of a submarine.

A risk common to all torpedo types of all nations was the problem of a circular run. These were rare, completely unpredictable, and with uncertain causes. Across all US torpedo types, circular runs happened less than 1% of the time but they were so threatening to the submarine itself that the possibility was always taken seriously. There is only one known instance of a Mark 18 torpedo circling back and damaging the submarine that launched it. On 25 Oct 1944, the USS Tang off Putian, China was struck in the stern by her own Mark 18 torpedo on a circular run that sank the boat. Seventy-eight lives were lost with only nine survivors.

The absence of a visible wake made the Mark 18 a popular choice among submarine commanders for daylight attacks and even night attacks in bright moonlight. Despite arriving mid-way through the war and serving side-by-side with the faster and now-reliable Mark 14, the Mark 18 still accounted for 30% of the torpedoes launched by US submarines in World War II and was responsible for sinking several thousand tons of shipping. The basic design remained in service into the 1950s when it was surpassed by faster and more dependable designs.

Sources:
United States Navy
Naval Postgraduate School, Monterey, California; Mark XIV Torpedo Case Study by David Matthews, 2011
Strategy Bridge - Michael J. Hennelly, 8 Feb 2018
Defense Media Network
Military History Online
Drachinifel Naval Historiographer YouTube Channel; The Mark 14 Torpedo - Failure is Like Onions, Feb 2020
The History Channel
SubSoWesPac.org
The Submarine Review; Oct 1996
Naval Weapons of the World (navweaps.com)
Hackaday Blog
Warfare History Network
The National Interest
The Pacific War Online Encyclopedia
San Francisco Maritime Museum
Julius Augustus Furer: Administration of the Navy Department in World War II
Stephen Moore: Presumed Lost: The Incredible Ordeal of America's Submarine POWs during the Pacific War
Weapons and Warfare
Naval Weapons of the World (navweaps.com)
San Francisco Maritime Museum
Wikipedia ww2dbase

Last Major Revision: Dec 2023

Mark XVIII Torpedo Interactive Map

Photographs

Mark XVIII Timeline

2 May 1942	The United States Navy placed an order for 2,000 Mark 18 torpedoes before the design had been finalized or tested.
13 Sep 1943	USS Wahoo departed Midway Atoll, starting her seventh war patrol. Based on the poor performance of the Mark 14 torpedoes on his earlier patrols, Wahoo captain Commander Mush Morton specifically requested to outfit his boat for this patrol exclusively with the new and not combat-tested electric Mark 18 torpedo.
21 Sep 1943	In the first successful use of the electric Mark 18 torpedo in combat, USS Wahoo sunk the Japanese merchant fishing vessel Hokusei Maru in the Sea of Ohkotsk.
22 Jan 1944	Gato-class submarine USS Silversides arrived at Pearl Harbor, Hawaii and commenced normal two-week refit. During this refit, Silversides’ after torpedo room was modified to accommodate the improved version of the Mark XVIII electric torpedo.
8 May 1944	Gato-class submarine USS Silversides arrived in her patrol area off Guam, Mariana Islands and almost immediately detected a convoy of six or seven Japanese ships departing Apra Harbor. Silversides fired four Mark XVIII electric torpedoes (her first of the war) and scored one hit, with unobserved results due to depth charging counterattack.
25 Oct 1944	USS Tang attacked a Japanese transport, but the Mark 18 electric torpedo she fired circled back and hit Tang, sinking her. Only 9 of the crew of 83 survived the sinking.

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