DEFENSIVELY EQUIPPED MERCHANT SHIPS - D.E.M.S. or "The Arming of Merchant Ships in WWII"


Please Note: I have based this information primarily on two sources: The Unknown Navy by Robert G. Halford, published by Vanwell Publishing, St. Catharines, Ontario, in 1995 and from The Naval Service of Canada: Volume 2 published by the Queens Printer, Ottawa in 1952.

This photo of the Defensively- Armed-Merchant Ship S.S. Point Pleasant Park, is taken from The Unknown Navy: Canada's World War II Merchant Navy by Robert G. Halford.

In anticipation of another European conflict Canadian and British war planners were examining as early as 1938 the possibility of arming merchant ships. In late August 1939 Great Britain notified Canada that, with war imminent, they were proceeding with equipping merchant shipping with defensive armaments and munitions in peacetime. On 3 September, 1939, the day WWII began, Germany declared that every vessel of the British mercantile marine was to be regarded as a warship. Since it was very unlikely that Germany would draw a fine line distinction between British and Canadian ships, Canada, on 25 September, 1939, by an Order In Council, authorized the defensive arming of 15 Canadian-registered merchant ships.

Due to shortages of Admiralty equipment, merchantmen were often forced to go to sea carrying only token armaments before the end of 1939. The supply of machine-guns was particularly inadequate. Ships were provided with armament as far as the supply situation permitted, but a considerable time elapsed before every ship could be equipped with some sort of weapon. Ocean-going ships had the first preference, and many of the smaller coasters and fishing vessels were still entirely devoid of any means of defence when the enemy commenced his aircraft attacks in the North Sea and elsewhere. In addition, shortages in trained personnel made it impossible to place a naval gunnery rating in each vessel, to take charge of the armament; and during that period merchant seamen often had to do the job as best they could. As a stop-gap the Army was called on to assist, and on the 27th February, 1940 arrangements were made with the War Office whereby the A/A armament of coasters was provided or augmented by two soldiers, with a Bren or a Lewis gun, to such vessels as could accommodate them. This arrangement was originally intended to last only two or three months, but it was found so satisfactory that it was expanded still further and eventually became permament.

At first, the only machine-gun available was the Lewis gun, and in order to improve the defensive protection of merchant ships it was arranged that those Army Bren gun teams who were acquainted with the Lewis gun should give the necessary instructions to the crews of the vessels in which they were embarked. An extra Lewis gun, if available, was provided, and this was to be retained on board when the soldiers disembarked. As supplies improved British fishing trawlers were armed with a Lewis gun, the good use of which made by many of them tended to keep the enemy aircraft at a greater height. Some, however, were caught napping, and in March 1940 Port Fishery Captains were instructed to impress on all concerned the necessity for having a gunner in each watch so that fire could be opened at once in case of attack. On 7th March, 1940, a single low flying, twin-engine aircraft dropped three bombs near the S.S. Lormont and two more near the S.S. Dover Abbey while machine gun fire was opened on these and other ships, in the Downs. No damage or injuries were sustained. A vigorous reply was made with A/A Lewis and Bren guns, which drove the enemy off. On 9th January, 1940, the enemy commenced air attacks with bombs and machine guns on convoys and shipping generally. Fishing and light vessels were not immune, and Allied and neutral were attacked indiscriminately, while firing on survivors in open boats was a common practice. The R.A.F. were unable at first to afford much protection, and the only counter-measures were a meagre scale of A/A defence. As from 9th March, 1940, merchant ships and fishing vessels at sea between the East Coast and the mine barrage were authorized to engage by day and night any aircraft not recognized as friendly approaching them within gun range (850 yards), and aircraft were warned not to approach within 1,500 yards of ships.

The defensive equipping of merchant ships was carried out at a reasonably satisfactory rate at Southampton with 17 ships completed in March and April, 1940 and 25 other vessels were equipped with Lewis guns. A Degaussing Establishment was set up and in March 1940 17 ships were completed by coiling and 13 by wiping ("Coiling" consists of fitting a permament cable round the ship, the supply of current being from the ship's dynamo. "Wiping" was a shorter operation, in which a strong current was passed through a temporary cable round the ship from an outside source. Both processes were for the purpose of demagnification.). Degaussing was also carried out at Portland, where there was, in addition, a degaussing (D.G.) range over which ships could be tested.

The business of arming merchantmen involved more than merely attaching the weapons to the ships. Due to the vibrations from firing and the metal stress created, reciprient vessels needed to be strengthened (or stiffened). The installation of weapons reduced the cargo capacities by an equivalent weight. For instance, the 12-pounder forward gun and mounting weighed 7,000 pounds. The amount of dead-weight DEMS entailed represented 75 to 100 tons in ocean-going ships. Initially, in Canada, 38 ships were selected for stengthening but work progressed slowly. After the war began Canada announced that all new vessels over 500 tons gross would be stiffened, those up to 1,000 tons gross stiffened to allow for one gun aft, and those over 1,000 tons gross for one low-angle gun aft and one high-angle gun in any position. At error in judgement at first placed tankers in a low priority. Minesweeping paravanes were later added as well as deguassing equipment. Due to a strict allied interpretation of the "Articles of War" there was a problem of whether naval DEMS personnel should be designated "deck hands" or "supernumeraries" since, if classified as military, the vessel could be classified as a warship. Trained navy personnel were thus given a lower rating and pay than their equivalents in the regular service. In the beginning there was no DEMS training facilities for navy or merchant seamen who were to be assigned the role of supporting personnel. For merchantmen, training was at a "hands-on" level and only when the weapons became available. As time progressed training establishments were established in eight Canadian centres.

While it may be said the civilian seamen were inadequately trained and inefficient at weaponry, needing to be guided by the navy ratings, the naval personnel had their difficulties as well. Most were inexperienced seamen having volunteered straight from basic training. There was no screening process, "if you volunteered, you were in". A further seagoing problem was the reluctance of ships' masters to release crewmen from their shipboard duties for DEMS stations. Another problem that developed was that DEMS ratings were being increasingly required to assume ships' duties, including stoking. In numbers, it was decided, in the case of the 10,000-ton Park ships, for instance, that there should be a minimum of 10 naval personnel but Admiralty requirements cut this to 9 and later as low as 5. By comparison, similarly armed US ships carried a USN complement of 24. With the establishment of training facilities a lack of interest was discovered on the the part of merchant seamen. This was partially solved by the granting of a $2 gratuity to each man that qualified. Prior to this arrangement their invovement was purely voluntary, except in an emergency, and they were paid at merchant service rates of pay. An illustration of this situation involved the British merchant men in the Pacific theatre in the last months of the war. British supply ships, unlike their US counterparts, were not naval ships and were crewed by non-military personnel. They were paid at their regular wage level, receiving no combat compensation. Due to the hazards involved matters finally reached a head when crews refused to offload at sea, a duty beyond their normal function. The RN was faced with a serious dilemna, since as civilians, they were not subject to the Articles of War and could not be charged with mutiny. The matter was finally resolved by placing naval storesmen aboard to handle this responsibility.

Halifax became an important centre for the training of seamen and ratings responsible for manning defensive equipment in merchant ships. Late in 1943 a firing range was established at Osborne Head. The range was equipped with a look-out tower, a small magazine, and concrete firing platforms for guns and rocket weapons. Amongst the essential training elements were "Dome Teachers". The Domes were large hemispheres (about 20 foot radius) which, by means of a combination of special interior lighting giving the illusion of infinite sky, and the projection on a Dome's interior surface of moving images of aircraft in various modes of attack, were used to instruct in such basic aiming techniques as leading the target. The course for Navy DEMS gunners was an intensive eight weeks at Halifax and HMCS Cornwallis. The personnel were trained with detailed knowledge of the mechanics of the many weapons they were expected to use, as well as skill in their operation and maintenance. The training received by merchant seamen, however, were only given a two-day general course and had to requalify every four months. Upon graduation they were given a "Merchant Navy AA Gunnery Course Certificate". A merchant gunner illustrated his duty at a Lewis AA gun by saying that he always took along a hammer, a chisle, and a screwdriver since the weapon often jammed, usually after one burst.

By 1944 a typically armed Victory ship carried : "At the bow was a 12-pounder HA/LA gun intended primarily for use against surface vessels or surfaced submarines. At the stern, atop the deckhouse for the seamen's/firemen's messes was a 4-inch HA/LA gun that could be equally effective against surface or air attacks. Also atop the same deckhouse, on an elevated mounting immediately behind the 4-inch gun, was a Pillar Box, an anti-aircraf t rocket weapon which was armed with twenty (20) rail-launched 2-inch high explosive rockets in racks, ten (10) on each side. On some ships, a 40-mm Bofors AA or a 20-mm Oerlikon gun was an alternative. Between the bow and stern extremities of the ship where the heavy weapons were positioned, were no less than eight (8) armoured gun tubs for light automatic, primarily AA, weapons, six (6) of which were 20-mm Oerlikon AA guns. Two gun tubs were located port and starboard at the aft end of the boat deck; two were port and starboard on the wings of the upper bridge; two further tubs were situated port and starboard of the foremost deckhouse. The two remaining tubs, which were intended for Twin .50-inch machine guns (intended to counter attacks by E-boats), were port and starboard immediately ahead of the forward exremities of the captain's bridge deck. "The "armour" that afforted a measure of protection against shrapnel and small arms fire for the gun tubs was a sandwich of steel plate with a thick asphaltic filling. A similar shielding also covered the front of the navigating bridge, the ship's command centre.

"The ships' anti-aircraft weaponry was rounded out with two Fast Aerial Mines (FAM) mounted port and starboard near the funnel. Most ships additionally carried the Parachute And Cable (PAC), similar to the FAM but lacking a bomb and trailing only about 400-feet of cable, about half that of FAM. "The FAM was a strange devise which comprised a propelling rocket and some 1,000-feet of light wire cable at the end of which was afixed an explosive devise, or mine. When fired, the rocket trailed the wire cable into the air in front of the attacking aircraft. On reaching optimum altitude, two parachutes were automatically deployed, a large one at top of the cable and a smaller one at the lower end. The concept was that a strafing aircraft would fly into the trailing wire as it slowly descended. Once snagged, the wire would be dragged by the larger parachute until the mine contacted the aircraft's structure.

"These ships also carried several passive DEMS devises amongst which were deguassing equipment as a countermeasure to magnetic mines. "On either side of the foredeck were stowed the minesweeping paravanes.
This photo is from S.C. Heal's A Great Fleet of Ships: The Canadian Forts and Parks. It shows the paravane gear and anti-torpedo nets on a new Canadian-built cargo vessel. The photo is from the collection of Captain Hill Wilson. A Great Fleet of Ships is published by Vanwell Publishing, St. Catharine's, Ontario, c. 1999.
Their purpose was to be towed by cables attached to the large A-frame projecting from the ship's bow. When the anchor cable of a submerged mine was snagged by a paravane tow cable, it was diverted along the cable by the ship's forward motion into the paravane's cutting jaws. Released from its anchor, the severed mine then popped to the surface where attempts to explode it, usually by small arms fire, would be made. "A prominent recognition feature was the towering (about 75-feet above deck level) booms for the torpedo nets (designated Admiralty Net Defences [AND] ). Normally stowed in the vertical position against the ends of the mast crosstrees, the booms pivoted from base attachments on each side of the fore and aft masthouses. Deployment involved lowering the booms and winching the nets forward from the after booms. The steel mesh curtains' function was to entangle or divert attacking torpedoes. When in position, to increase the spread of the nets the foremast booms were swept forward while the mainmast booms were swept aft. The protection they afforded covered approximately four-fifths of the ship's length. This included the vital engine room and most if not all of the crew's quarters. To deploy or stow the clumsy gear could be hard, dangerous work, even in the best of sea conditions. The nets also affected ship performance. When stowed, their weight added an element of top-heaviness, increasing rolling propensity. When deployed (in convoy), the added drag reduced speed by about 2-knots, a significant slowing for a vessel that under ideal conditions usually achieved only 11-knots."

In addition to the regularly equipped merchant ships were two specialized types: the Catapult Aircraft Merchant Ships (CAMS) and the Merchant Aircraft Carriers (MACs). These two types remained merchant cargo vessels with civilian crews and officers while the air crews and maintenance personnel were Navy. In the case of the CAMS, a ship carrying a foward catapult with an attached Hurricane fighter plus one in storage and no landing-on facilities, the Navy personnel were required to wear civilian gear while at sea. The decision to launch was left to the discretion of the ship's master. The MACs had a full flight deck (and in the case of dry cargo vessels, a hangar). The launch decision being borne by the Convoy Commander.

An example of the valour of the DEMS vessels is illustrated by the engagement in the Indian Ocean between a small convoy and two Japanese Armed Merchant Cruisers (primarily civilian manned). The convoy escort, a single tug, and only armed with a 4-inch gun turned towards the cruisers to permit the two or three ship convoy time to escape. One of the merchantmen, a tanker, and only armed with a single stern mounted 5-inch gun, turned back to assist her escort. Together they succeeded in sinking one of the cruisers and driving the other one off before proceeding on to their destination.

You can reach me, Cliff McMullen, at .

Thanks are due to Maureen Venzi for her assistance in putting together this page. I strongly recommend paying a visit to Maureen's Allied Merchant Navy of World War Two Website.

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