Merchant raider

Merchant raiders are armed commerce raiding ships that disguise themselves as non-combatant merchant vessels. Germany used several merchant raiders early in World War I, and again early in World War II. The most famous captain of a German merchant raider, Felix von Luckner, used a sailing ship SMS Seeadler for his voyage during World War I.

Germany sent out two waves of six surface raiders each during World War II. Most of these vessels were in the 8-10,000 ton range. Many of these vessels had originally been refrigerator ships, used to transport fresh food from the tropics. These vessels were faster than regular merchant vessels&mdash;important for a warship. They were armed with six 15cm (5.9 inch) naval guns, some smaller calibre guns, torpedoes and reconnaissance seaplanes. Some carried mines and were fitted for minelaying. Some captains were very creative about disguising their vessels to masquerade as allied or neutral merchants. Italy used four "Ramb" class ships as auxiliary cruisers in World War II.

These commerce raiders were unarmoured because their purpose was to attack merchantmen, not to engage naval units in open combat. Also it would be difficult to fit armour to a civilian vessel. Eventually most were sunk or transferred to other duties.

British Armed Merchant Cruisers were generally adapted from passenger liners, and were larger than the German vessels.

During World War I, the Royal Navy deployed Q-ships to engage German U-boats. Although Q-ships were warships pretending to be merchant ships, their mission of destroying enemy warships was significantly different to the raider objective of disrupting enemy supplies.