The Effectiveness of Torpedoes and Mines in World War II

Author

Turner, Mike

Subjects

History - WW2

Tags

Torpedo, Ship losses, Mines

RAN Ships

None noted.

Publication

March 2014 edition of the Naval Historical Review (all rights reserved)

By Mike Turner

Mike Turner graduated from Sydney University with a degree in Science and an Honours degree in Aeronautical Engineering. After qualifying as a Ships Diver in 1957 he joined the RAN Mine Countermeasures Development Unit (MCDU) at HMAS Rushcutter to develop a towed diver search system. Transferring to the RAN Experimental Laboratory (RANEL) he was involved in mine identification and the ‘half-necklace’ ship’s bottom search for Ships Divers. Working in just about all areas of mine countermeasures (MCM) included the observation and analysis of multi-national MCM exercises. The final project before retiring in 1990 was the development of MCM equipment, particularly ‘Dyad’ magnetic sweeps, to enable the RAN to use ‘Craft of Opportunity’ as minesweepers.

Submarine Torpedoes and Aerial Mines

Submarine torpedoes and aerial mines were the two major weapons used against warships and merchant ships in World War II, and were used to good effect by America, Britain and Germany. In contrast Japanese submarines sank very few Allied ships, and Japan lacked an aerial mine for mining in Allied held waters (offensive mining).

All losses stated in this article must be treated with due caution, and generally refer to ships over 500 tons.

Ships sunk by torpedoes

The torpedo is the ‘weapon of choice’ for submarines attacking ships. Japanese submarines sank 18 ships over 500 tons in Australian waters, and they were all sunk by torpedoes.¹ In a listing of 1,242 Merchant Navy ships sunk by U-boats 1,141 (92%) were sunk by torpedoes and only 101 (8%) were sunk by gunfire or the combination of torpedoes and gunfire.²

The major submarine offensive by the German U-boats in the ‘Battle of the Atlantic’ sank 2,788 ships and, assuming that 92% were sunk by torpedoes, 2,561 ships were sunk by German torpedoes.³

Ships sunk by mines

The largest offensive mining operation in World War II was the laying of about 50,000 British ground mines in NW Europe by British aircraft for the loss of approximately 500 aircraft.⁴ British mines sank 1,043 Axis ships compared to about 432 Axis ships sunk by British submarines.⁵

From a British viewpoint mines accounted for more shipping losses than submarines. This is probably the genesis of the common myth that ‘In World War II mines sank more ships than any other weapon.’ More ships were sunk by German torpedoes than were sunk by the mines laid by all countries. Whilst the table on the following page does not show losses due to torpedoes alone it gives a reasonable indication of the relative losses due to torpedoes and mines.

Enemy ships sunk in World War II

Minefield effectiveness

The number of mines laid per ship sunk is often used as a criterion for minefield effectiveness. It is easy to derive this simplistic statistic, but it normally lacks relevance. A minefield has the capability to sink ships or submarines, and this capability makes its threat credible. However the real function of a minefield is not the sinking of ships. It is the control of the movement of enemy ships and submarines, and is difficult to quantify. The aim of tactical mining may be to control the movement of shipping such that it is more vulnerable to attack by other means, for example divert shipping into deeper water where it is more vulnerable to submarines. Control of an enemy’s shipping results from the enemy’s perception of potential damage rather than the number of mines and mine technology per se. It is human nature to overestimate the threat from unseen weapons such as mines. The mine has a psychological warhead, and ‘the real effect of a minefield derives from a more subtle influence- an exaggerated fear. Minefields work more on the mind than on ships.’¹⁰

No ships are sunk by mines when an ideal mining operation prevents any movement of shipping. A classic example of such an operation was a USN mining operation after 32 ships at Palau Atoll in the Caroline Islands were located on 30 March 1944. That night 78 Avenger torpedo-bombers from the carriers US Ships Lexington, Bunker Hill and Hornet ‘bottled up’ these targets by each laying an American Mk 10 moored mine or an American Mk 25 ground mine.¹¹ Although an attack next day seemed to be assured no ship attempted to flee to safety that night due to the psychological warhead of the mines. The carrier aircraft returned next day and 23 vessels over 500 tons were sunk by bombs and torpedoes, the average size being 4,425 tons.¹² The other nine vessels had also been reported as sunk, and presumably were all under 500 tons.¹³

A more recent example of an effective mining operation that did not sink any ships was at Haiphong during the Vietnam War. The initial minelay was by three A6-A and six A7-E aircraft from USS Coral Sea on 9 May 1972, and each aircraft laid four American Mk 52 ground mines with an arming delay.¹⁴ The thirty two ships at Haiphong were assured by American President Richard Nixon that these mines would not arm for three days, and five ships departed.¹⁵ The other 27 ships chose to stay in port, and traffic flow was reduced from 40 ships a month to zero. Mining was sustained and had significant psychological, political and military impact at the time. No ship entered the shipping channel until TF 78 swept a channel in 1973 (Operation END SWEEP). This American clearance operation was a vital lever in obtaining the release of American POWs.¹⁶

The effectiveness of a strategic minefield can be expressed as the reduction in traffic as a percentage of the traffic prior to mining. Operation STARVATION was the attrition strategic mining of Japanese and Korean home waters by American aircraft during World War II. It was in five phases. In Phase One 2,030 ground mines were laid from 27 March 1945 to 3 May 1945, and 12,321 ground mines had been laid by US Army Air Force (USAAF) and USN aircraft when Phase Five concluded on 5 August 1945. The effectiveness of this operation is demonstrated in the figure, where the width of a ‘route’ in the figure is proportional to the average tons of shipping per day. Mining in the vital Shimonoseki Strait was 92 percent effective, traffic being reduced from about 800,000 tons per month to about 60,000 tons per month. Mining was completely effective along the east coast of Japan, and all the ports were closed.¹⁷

It is rarely possible to quantify the effectiveness of tactical mining conducted to support other operations. This would require a comparison of enemy losses for the actual scenario (which includes tactical mining) with enemy losses for the hypothetical scenario in which there is no tactical mining.

Summary

In World War II torpedoes sank more ships than mines. However mine effectiveness is not measured by ships sunk or damaged. It is measured by the psychological impact of a weapon that waits and by the control of the movement of shipping such a threat imposes The minefield is a unique weapon in that it can pose a threat without any forces being present and can be used to enforce a blockade without risking forces. A minefield can deny free movement to enemy surface and submarine forces as well as neutral shipping.

The threat of mining can cause an enemy to divert very large resources from the ‘sharp end’ to defensive mine counter-measures (MCM). In World War II the total MCM effort for America, Britain, Germany and Japan was 3,230 ships and 146,000 men. This included the German effort of ‘46,000 men and officers, 1,276 sweepers, 170 boats and 400 planes’.¹⁸ By 1945 German MCM effort comprised 40 percent of all naval activity.¹⁹

1   Ships attacked off the Australian coastline by Japanese submarines. www.ozatwar.com /japsubs/shipssunk.htm (26 September 2013). (Vessels over 500 tons)

2     Merchant Navy Losses, www.battleships-cruisers.co.uk/merchant_navy_losses.htm (12 August 2013).

3     Ships hit by U-boats in WWII, www.uboat.net. (14 August 2013)

4     J C Cowie, Mines, minelayers and minelaying, Oxford University Press, London, 1949, p164.

5     Includes many Italian ships. See Campaign summaries of World War 2. British submarines at war. www.naval_history.net/WW2 CampaignBritishSubs2.htm (14 August 2013).

6     J C Cowie, Mines, minelayers and minelaying, London, Oxford University Press, 1949, p166.

7     The Joint Army-Navy Assessment Committee NAVEXOS P 468, Japanese naval and shipping Losses during World War II by all causes, 1947, www.history.navy.mil/library/online/japaneseshiploss.htm‎ (11 August 2013). (Vessels over 500 tons)

8   See U.S. Merchant Ships Sunk or Damaged in World War II, www.usmm.org/mineships.html (14 August 2013) and Casualties, Navy and Coast Guard Ships, WW II, www.history.navy.mil/faqs/faqs82-1.htm (30 April 2005).

9   Ships sunk by Japanese submarines, http://en.wikipedia.org/wiki/Category:Ships_sunk_by_Japanese_submarines (15 August 2013). This source lists 33 ships, and excludes 11 of the 18 ships sunk in Australian waters. (Vessels over 500 tons)

10 JC Bartholomew and WL Greer, Psychological aspects of mine warfare, Professional Paper 365, Center for Naval Analyses, Virginia, 1982, p5.

11 BR 1736 (50) (5), The Blockade of Japan, Admiralty, 1957 as CB 3303 (5), p35.

12 The Joint Army-Navy Assessment Committee NAVEXOS P 468, Japanese naval and shipping Losses during World War II by all causes.

13 R.C. Duncan, America’s Use of Sea Mines, US Government Printing Office, Washington, 1962, p39.

14 USS Coral Sea CVA 43. www.navysite.de/cvn/cv43.htm (2 October 2010)

15 J.S. Chilstrom, thesis, Mines Away! The significance of US Army Air Forces Minelaying in World War II, Chapter 6, Maxwell Air Force Base, Alabama, 1992. www.maxwell.af.Mil/au/aul/aupress/SAAS_Theses/SAASS_Out/Chilstrom/ Chilstrom_about_out.htm (13 December 2004).

16 Operation End Sweep, www.geocities.com/Pentagon/Bunker/2170/operationendsweep.html, (28 November 2004).

17 BR 1736 (50) (5), The Blockade of Japan, pp126, 155.

18 G.K. Hartman and S C Truver, Weapons That Wait, Annapolis, Naval Institute Press, 1991, p236.

19 J.S. Chilstrom, thesis, Mines Away! The significance of US Army Air Forces Minelaying in World War II, Chapter 2.