Defensively Equipped Merchant Ships

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Defensively Equipped Merchant Ship (DEMS) was an Admiralty Trade Division program established in June, 1939, to arm 5,500 British merchant ships with an adequate defence against enemy submarines and aircraft. The acronym DEMS was used to describe the ships carrying the guns, the guns aboard the ships, the military personnel manning the guns, and the shore establishment supporting the system.[1]

Contents

[edit] Background

Britain had begun arming merchant ships during the Napoleonic Wars to prevent capture by enemy commerce raiders and privateers while ferrying valuable cargo back from the Far East. The East Indiamen class of ships where therefore constructed from the ground up with heavy armament in mind, making them equivalent of naval ships of the line. Once the threat passed, East Indiamen were replaced with faster and lighter ships such as clippers.

[edit] World War I

During the First World War, Britain once again armed its merchant ships to help defend them against U-boats. A single stern gun, equivalent to what a submarine might carry, was mounted; and civilian captains were encouraged to flee and shoot back from their more stable gun platform. 766 civilian ships had been armed by December, 1915.[2] Arming of merchant ships gave Germany an excuse for moving toward unrestricted submarine warfare.[3]

The first merchant ship lost to U-boats was an 866-ton British steamer outbound from Grangemouth to Stavanger with a cargo of coal, iron plate, and oil. Glitra was stopped by U-17 on 20 October 1914; and a boarding party gave Glitra's crew time to disembark into lifeboats before sinking the ship by opening valves to flood holds with sea-water. The procedure followed customs originated by surface ships. International maritime law required the naval vessel to make adequate provisions for the safety of the merchant crew and passengers before sinking their ship.[4]

Imperial Germany focused use of U-boats against merchant shipping in response to British blockade of German merchant shipping by declaring the entire North Sea a war zone on 2 November 1914. On 5 February 1915 Germany published notice declaring a war zone in all waters around Great Britain and Ireland. Within that zone, Germany conducted unrestricted submarine warfare against merchant ships from 18 February 1915 without warning and without regard to safety of their crew.[5]

U-boats still conformed to earlier conventions of stopping ships when possible, but the typical submarine mounted only a single gun. The two procedures for sinking merchant ships were compared in 1915. Merchant ships escaped 42% of torpedo attacks made without warning, in comparison to 54% escaping from conventional surface attempts to stop the ship.[6] Guns aided escape and approximately one submarine per month was sunk (most by Q-ships) while attempting a surfaced stop.[7]

The number of civilian merchant ships armed with anti-submarine guns rose to 1749 by September of 1916 and 2899 by February of 1917.[8] The United States responded to unrestricted submarine warfare by severing diplomatic relations with Germany on 3 February 1917. A filibuster in the United States Senate temporarily delayed President Woodrow Wilson's proposal on 26 February 1917 to arm United States merchant ships, but arming started in March under an executive order.[9]

[edit] World War II

Old naval guns had been stored since 1918 in major seaports for possible use during future hostilities. During the Second World War, the objective was to equip each ship with a low-angle gun mounted aft as defence against surfaced submarines and a high-angle gun and rifle-calibre machine guns for defence against air attack.[10] 3,400 ships had been armed by the end of 1940;[11] and all ships were armed by 1943.[12]

1915 photo of 12-pounder gun later available for DEMS.
1915 photo of 12-pounder gun later available for DEMS.

The low-angle guns were typically in the 3-inch to 6-inch range (75-150 mm) depending on the size of the ship. Rifle-caliber machine guns were augmented or replaced by 20 mm Oerlikon as they became available. The High-Angle QF 12pdr mount was the most common anti-aircraft gun, and later ships sometimes received 40 mm Bofors guns.[13]

Untrained gunners posed significant risk to friendly aircraft in the absence of efficient communications.[14] DEMS guns were manned by 24,000 Royal Navy personnel and 14,000 men of the Royal Artillery Maritime Regiment. One-hundred-fifty-thousand merchant sailors were trained to assist by passing ammunition, loading, and replacing casualties among the military gun crew.[15] Royal Artillery personnel had initially provided anti-aircraft protection by bringing their own machine-guns aboard ships operating close to the British Isles.[16] DEMS gunners were often retired military personnel and young "Hostilities Only" ratings commanded by a petty officer or Royal Marine sergeant. Large ships sometime embarked a junior naval officer to command the DEMS gunners.[17]

Canada placed guns on 713 ships.[18]

5"/38 caliber dual-purpose Mark 37 gun mount used on merchant ships. This example is preserved at the National Museum of the Pacific War.
5"/38 caliber dual-purpose Mark 37 gun mount used on merchant ships. This example is preserved at the National Museum of the Pacific War.

[edit] United States

Neutrality Acts prevented arming of United States flagged merchant ships until 17 November 1941, although American-owned ships under Panamanian registry had been armed earlier.[19] Guns were manned by United States Navy Armed Guard. United States began equipping ships of other nations with guns and United States Navy Armed Guard on 24 January 1942.[20] United States policy was stated by the Vice Chief of Naval Operations on 19 August 1942: "Ships sailing independently should be armed. Ships sailing in regularly made-up convoys, other than ships bound to North Russia or tankers en route to the United Kingdom, may sail unarmed if the urgency of delivery of their cargo warrants it."[21]

The United States followed the British practice of a single large gun aft. Early United States installations included low-angle 4"/50 caliber guns (Mark 9) removed from old Wickes and Clemson class destroyers.[22] The first installations of dual-purpose 5"/38 caliber guns began in September, 1942, on new ships over 10,000 tons.[23] Victory ships carried a 3-inch gun on the bow, 20 mm machine gun tubs port and starboard between the first and second holds; a 2nd pair of 20 mm guns on the bridge wings, a 3rd pair on the after edge of the superstructure, and a 4th pair between the after (Number 5) hatch and the 5"/38 caliber gun on the stern.[24]

[edit] See also

[edit] Notes

  1. ^ Hague 2000 p.VIII
  2. ^ Tarrant 1989 p.17
  3. ^ van der Vat 1988 p.124
  4. ^ Tarrant 1989 p.12
  5. ^ Tarrant 1989 pp.13-14
  6. ^ Tarrant 1989 p.22
  7. ^ Tarrant 1989 p.22
  8. ^ Tarrant 1989 p.37
  9. ^ Potter&Nimitz 1960 p.465
  10. ^ Hague 2000 p.101
  11. ^ van der Vat 1988 p.124
  12. ^ Middlebrook 1976 p.30
  13. ^ Hague 2000 p.101
  14. ^ van der Vat 1988 p.124
  15. ^ Morison 1975 p.301
  16. ^ van der Vat 1988 p.124
  17. ^ Hague 2000 p.102
  18. ^ van der Vat 1988 pp.138-9
  19. ^ Morison 1975 pp.296-7
  20. ^ Morison 1975 p.297
  21. ^ Morison 1975 p.301
  22. ^ Campbell 1985 pp.143
  23. ^ Morison 1975 p.301
  24. ^ Babcock&Wilcox 1944 pp.6-7

[edit] References

  • Babcock and Wilcox (April 1944). "Victory Ships". Marine Engineering & Shipping Review. 
  • Campbell, John (1985). Naval Weapons of World War Two. Naval Institute Press. ISBN 0-87021-459-4. 
  • Hague, Arnold (2000). The Allied Convoy System 1939-1945. Naval Institute Press. ISBN 1-55750-019-3. 
  • Hughes, Terry and Costello, John (1977). The Battle of the Atlantic. The Dial Press. ISBN 0-8037-6454-2. 
  • Middlebrook, Martin (1976). Convoy. William Morrow and Company. 
  • Morison, Samuel Eliot (1975). History of United States Naval Operations in World War II, Volume I The Battle of the Atlantic 1939-1943. Little, Brown and Company. 
  • Potter, E.B. and Nimitz, Chester W. (1960). Sea Power. Prentice-Hall. 
  • Rohwer, J. and Hummelchen, G. (1992). Chronology of the War at Sea 1939-1945. Naval Institute Press. ISBN 1-55750-105-X. 
  • Tarrant, V.E. (1989). The U-Boat Offensive 1914-1945. Sterling Publishing. ISBN 1-85409-520-X. 
  • van der Vat, Dan (1988). The Atlantic Campaign. Harper & Row. ISBN 0-06-015967-7.