The gun crew of a defensively equipped merchant ship during a drill at Halifax, Nova Scotia in 1942. A merchant seaman is passing a shell to the Royal Navy gunners.
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.
In the eighteenth and nineteenth centuries, European countries such as Spain, France, the Netherlands and Britain armed their merchant ships to prevent capture by pirates, enemy commerce raiders and privateers when they conducted overseas trade. The most heavily armed were ships carrying valuable cargo back from the Far East. For example, the East Indiamen class of ships were constructed from the ground up with defence in mind, with their heavy armament making them equivalent to naval ships of the line. Once the threat passed after the end of the Napoleonic Wars in 1815, armed merchant ships like East Indiamen were replaced with faster and lighter unarmed ships such as clippers.
The Admiralty chose to do likewise, starting with ther Royal Mail Steam Packet Company passenger liner RMS Aragon. She was due to carry naval guns from December 1912, but within the British Government and Admiralty there was uncertainty as to how foreign countries and ports would react. Many merchant ships had been armed in the 18th century and it had never been made illegal, but Britain feared that foreign authorities might refuse to let armed British merchant ships enter port. In January 1913 Rear Admiral Henry Campbell recommended that the Admiralty should send a merchant ship to sea with naval guns, but without ammunition, to test foreign governments' reaction. A meeting chaired by Sir Francis Hopwood, Civil Lord of the Admiralty agreed to put guns without ammunition on a number of merchant ships "and see what happens." Sir Eyre Crowe was at the meeting and recorded "If nothing happens, it may be possible and easy, after a time, to place ammunition on board."
In March the policy was made public, and in April it was implemented. On 25 April 1913 Aragon left Southampton carrying two QF 4.7-inch (120 mm) naval guns on her stern. The Admiralty planned to arm Houlder Brothers' La Correntina similarly if the reaction were favourable. Governments, newspapers and the public in South American countries that Aragon visited took little notice and expressed no concern.
There was more criticism in Britain, where Commander Barry Domvile, Secretary to the Committee of Imperial Defence, warned that the policy undermined Britain's objection to the arming of German merchant ships. Domvile predicted that arming merchant ships would be ineffective, and would lead only to a second maritime arms race alongside the naval one.Gerard Noel, a former Admiral of the Fleet, told Churchill that were a merchant ship ever to fire its guns it could be accused of piracy. Churchill replied by drawing a distinction between merchant ships armed as auxiliary cruisers and those armed only for self-defence.
Privately Churchill was more concerned, and in June 1913 he directed Admiralty staff to "do everything in our power to reconcile this new departure with the principles of international law". However, the policy continued. Aragon's sister ship RMS Amazon was made the next DAMS, and in the following months further RMSP "A-liners" were armed. They included the newly built Alcantara, which in the First World War did indeed serve as an armed merchant cruiser.
World War I
During the First World War, Britain 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. Arming of merchant ships pushed Germany away from prize rules towards unrestricted submarine warfare, an important factor in bringing the United States into the war against Germany.
The US passenger steamer SS Kroonland in November 1917, showing camouflage paint and stern mounted gun.
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. SS Glitra was stopped by the German submarine 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 seawater. 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.
The German Empire 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.
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. Guns aided escape and about one submarine per month was sunk (most by Q-ships) while attempting a surfaced stop.
BL 4 inch Mk VII low-angle gun on a DEMS in 1943, an obsolete WWI gun typical of WWII DEMS armament
In 1941 the DEMS carried only one Thomson submachine gun, to be turned over on arrival in England, and a stripped Lewis gun for air defense only; one seaman per merchant ship. Old naval guns had been stored since 1918 in major seaports for possible use during future hostilities. In 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. 3,400 ships had been armed by the end of 1940; and all ships were armed by 1943.
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 Mk V mount was the most common anti-aircraft gun, and later ships sometimes received Bofors 40 mm guns.
Untrained gunners posed significant risk to friendly aircraft in the absence of efficient communications. DEMS guns were manned by 24,000 Royal Navy personnel and 14,000 men of the Royal Artillery Maritime Regiment. 150,000 merchant sailors were trained to assist by passing ammunition, loading, and replacing casualties among the military gun crew. Initially, Royal Artillery personnel provided anti-aircraft protection by bringing their own machine-guns aboard ships operating close to the British Isles. DEMS gunners were often retired military personnel and young "Hostilities Only" ratings commanded by a petty officer or Royal Marinesergeant. Large ships sometimes embarked a junior naval officer to command the DEMS gunners.
In 1944, during preparations for the invasion of France called Operation Overlord there was deep concern over the danger to Allied aircraft from the large number of DEMS involved in the landings. A request for volunteer aircraft recognition experts from the Royal Observer Corps produced 1,094 highly qualified candidates, from which 796 were selected to perform valuable aircraft recognition duties as seaborne volunteers.
These Seaborne Observers were organised by Group Commandant C.G. Cooke and trained at the Royal Bath Hotel Bournemouth before the volunteers temporarily joined the Royal Navy with the rank of petty officer (aircraft identifier). The volunteers continued to wear their ROC uniforms, but wore "seaborne" shoulder flashes and a Royal Navy brassard with the letters RN. During the D-day landings two "seaborne" observers were allocated to each of the defensively equipped merchant ships, both British and American vessels. The ROC volunteers were given direct control of each ship's anti-aircraft batteries, immediately reducing the previously high level of 'friendly fire', or 'blue on blue' incidents as they are now known. Their success is measured by a signal from Wing Commander P.B. Lucas, air staff officer who reported:
"The general impression amongst the Spitfire wings, covering our land and naval forces over and off the beach-head, appears to be that in the majority of cases the fire has come from warships and not from the merchant ships. Indeed I personally have yet to hear a single pilot report that a merchant vessel had opened fire on him"
Twenty two seaborne observers survived their ships being sunk, two lost their lives and several more were injured during the landings. The "seaborne" operation was an unqualified success and in recognition, His Majesty King George Vl approved the wearing of the "seaborne" flash as a permanent feature of the uniform. In addition, ten "seaborne" members were mentioned in despatches. After the invasion and just before his death Air Chief Marshal Trafford Leigh-Mallory wrote the following to be circulated to all ROC personnel:
"I have read reports from both pilots and naval officers regarding the Seaborne volunteers on board merchant vessels during recent operations. All reports agree that the Seaborne volunteers have more than fulfilled their duties and have undoubtedly saved many of our aircraft from being engaged by our ships guns. I should be grateful if you would please convey to all ranks of the Royal Observer Corps, and in particular to the Seaborne observers themselves, how grateful I, and all pilots in the Allied Expeditionary Air Force, are for their assistance, which has contributed in no small measure to the safety of our own aircraft, and also to the efficient protection of the ships at sea.
The work of the Royal Observer Corps is quite often unjustly overlooked, and receives little recognition, and I therefore wish that the service they rendered on this occasion be as widely advertised as possible, and all units of the Air Defence of Great Britain are therefore to be informed of the success of this latest venture of the Royal Observer Corps."
As of 2010 there is a Seaborne Observers’ Association for the dwindling number of survivors. Former Air Vice-Marshal George Black, a former Commandant ROC, is the honorary president.
5"/38 calibre dual-purpose Mark 37 gun mount used on American merchant ships. This example is preserved at the National Museum of the Pacific War.
The Merchant Marine Act of 1936 identified mariners aboard United States flagged merchant ships as military personnel in time of war 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. 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; and approximately 145,000 USN armed guards ultimately sailed aboard 6,236 merchant ships. 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."
Rohwer, J; Hummelchen, G (1992). Chronology of the War at Sea 1939–1945. Annapolis, MD: Naval Institute Press. ISBN 1-55750-105-X.
Seligmann, Matthew S (2012). The Royal Navy and the German Threat 1901–1914: Admiralty Plans to Protect British Trade in a War Against Germany. London and Oxford: Oxford University Press. p. 132. ISBN 978-0-19-957403-2.
Slader, John (2009). Fourth Service: Merchantmen at War, 1939–45. New York: Brick Tower Press. ISBN 978-1-899694-45-7.
Marcus, Alex (1986). "DEMS? What's DEMS?": The story of the men of the Royal Australian Navy who manned defensively equipped merchant ships during World War II. Bowen Hills, Qld.: Boolarong Publications. ISBN 0-86439-012-2.