Defensively equipped merchant ship

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.

After the end of the Napoleonic Wars in 1815, these were replaced for some of the balance of the 19th century with faster and lighter unarmed ships such as clippers that, in theory, could outrun any threat when blockade running or carrying smaller quantities of the most valuable cargoes long distance.

From the turn of the 20th century, growing tensions between Europe's Great Powers included an Anglo-German naval arms race that threatened the security of merchant shipping.

In December 1911 a memo from Winston Churchill, recently appointed as First Lord of the Admiralty, proposed that the utility or otherwise of arming British merchant ships "for their own defence" be ascertained.

"[4] The ships being armed by the Kaiserliche Marine were passenger liners that were fast enough to serve as auxiliary cruisers, and they would indeed be used as raiders in WWI, though there were not as many as the British expected.

A second plan was to experiment with having civilian ships armed for their own protection, starting with the Royal Mail Steam Packet Company passenger liner RMS Aragon.

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.

[7] 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."

The latter method was how the first merchant ship lost to U-boats was sunk: This, the Glitra, was an 866-ton British steamer outbound from Grangemouth to Stavanger with a cargo of coal, iron plate, and oil.

She 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.

International maritime law required the naval vessel to make adequate provisions for the safety of the merchant crew and passengers before sinking their ship.

For that reason, despite pressure from naval authorities and public declarations of intent to attack with warning, crews preferred otherwise, sinking the majority of ships on the surface in accordance with cruiser rules up until the end of 1916.

[19] Nevertheless, the guns were mounted on the stern of vessels, transferred from one ship to another to ensure maximum use, and civilian captains were encouraged to flee while shooting back.

[16] While submarines were still scoring a high number of kills on the surface, the rising number of armed merchant ships was cited as a factor (alongside the more major point that they anticipated a swift victory by starving Britain) in the German Admiralty Staff's December 1916 Holtzendorff Memorandum,[21] leading to a second campaign of unrestricted submarine warfare.

[26] Initially, Royal Artillery personnel provided anti-aircraft protection by bringing their own machine-guns aboard ships operating close to the British Isles.

[24] DEMS gunners were often retired military personnel and young Hostilities Only ratings, commanded by a petty officer or Royal Marine sergeant.

[28] 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.

The volunteers continued to wear their ROC uniforms, but wore seaborne shoulder flashes and a Royal Navy brassard with the letters RN.

The ROC volunteers were given direct control of each ship's anti-aircraft batteries, immediately reducing the previously high level of friendly fire incidents.

Indeed I personally have yet to hear a single pilot report that a merchant vessel had opened fire on himTwenty two seaborne observers survived their ships being sunk, two lost their lives and several more were injured during the landings.

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.