Commerce raiders

Commerce raiding is a form of naval warfare used to destroy or disrupt logistics of the enemy on the open sea by attacking its merchant shipping, rather than engaging its combatants or enforcing a blockade against them. It is also known, in French, as guerre de course (literally, "war of the chase") and, in German, Handelskrieg ("trade war"), from the nations most heavily committed to it historically as a strategy.

Commerce raiding was heavily criticised by the naval theorist A.T. Mahan, who regarded it as a distraction from the destruction of the enemy's fighting power. Nevertheless, commerce raiding was an important part of naval strategy from the Early Modern period through the Second World War.

Usually, commerce raiding is chosen by a weaker naval power against a stronger, or by a nation with little ocean-going trade against one with a great deal. The best protection against a commerce raiding strategy is for merchant vessels to sail in convoy, protected by naval escorts.

The first sort of commerce raiding was for nations to commission privateers. Early instances of this type of warfare were by the British and Dutch against the Spanish treasure fleets of the 16th century, which resulted in financial gain for both captain and crew upon capture of enemy vessels ("prizes").

This quickly became a major commercial enterprise, with privateer vessels, often in groups, being outfitted by venture capital, with investors also sharing in the returns. The practice rapidly spread. A privateer was distinguished from a pirate by the letter of marque, by which the vessel was commissioned as a private man-of-war. Captured vessels and cargo were submitted, in Britain's case, to Admiralty courts, where they might be condemned for sale, or, if the captures were not found to be within the rules of war, they might be released, sometimes with awards for damages.

...
Wikipedia