Secret danger: Q-ships.

Wiki:

A Q-ship hidden deck gun

Q-ships or Q-boats were disguised merchant vessels that carried cannons, depth charges and antisubmarine equipment. They were used as a bait to attract and then sink German U-boats during World War I primarily by Britain and, later, during World War II predominantly by the United States. In the United Kingdom the vessels chosen for this service were code-named Q-ships by the Admiralty, but they were also known as Decoy Vessels, Special Service Ships or Mystery Ships. The Germans had similar ships called merchant raiders.


In the First Battle of the Atlantic, by 1915, Britain was in desperate need for a countermeasure against the U-boats that were strangling her sea-lanes. Convoys, which had proven effective in earlier times (and would again prove effective during World War II), were rejected by the resource-strapped Admiralty and the independent captains. The depth charges of the time were very primitive, and thus the only method of sinking a submarine was by gunfire or by ramming. The problem was luring the U-boat to the surface.
The solution to this problem was the creation of the Q-ship, one of the most closely-guarded secrets of the war. Their codename referred to the vessels' home port, Queenstown. These would be known to the Germans as a U-Boot-Falle ("U-boat trap"). The Q-ship would pose as an easy target for the U-boat but in fact carry hidden armament. A typical Q-ship would be an old-looking tramp steamer calmly sailing alone near an area where a U-boat was reported to be operating. By posing as a suitable target for the use of the U-boat's deck gun, the Q-ship would encourage the U-boat Captain to bring his vessel to the surface rather than use one of his expensive torpedoes, which were in short supply. The cargoes of the Q-ships would be wooden caskets and wood (e.g., balsa or cork) so even if torpedoed they would stay afloat, encouraging the U-boat to surface and use its gun. If necessary the crew could even stage an "abandon ship" routine. Once the U boat was in a suitable position the Q-ship would change rapidly, false panels would drop to reveal the hidden guns which would start firing. At the same time the White Ensign (Royal Navy flag) would be raised. With the element of surprise the U-boat could be quickly overwhelmed.

A cigarette card of a Q-Ship in action

Despite some spectacular actions and a great deal of romanticization, Q-ships were not particularly successful (see HMS Dunraven). In the course of 150 engagements they were only able to destroy 14 U-boats and damage another 60, at a cost of 27 Q-ships lost out of 200. Q-ships were responsible for only about 10% of all U-boats sunk, ranking them far below the use of mine fields in overall effectiveness. Neither of the German Q-Boats, Möwe and Wolf, had any success in destroying enemy submarines.


The automotive term Q-ship (or "Q-car"- in the U.S. "Sleeper") has subsequently been used to describe cars that have much higher than average performance but look like conventional, uninteresting family transport. As well as the ships, this term may also be reinforced by the United Kingdom's system of vehicle registration plate numbering - until recent years the first (previously the last) symbol on a British plate was a letter code for the year of manufacture, but for vehicles of uncertain or mixed age, a plate beginning with "Q" is used.

the ultimate road going Q-Ship: the 177 mph Lotus Carlton