A term originally accepted in international maritime law to indicate the practice of privateering, or the right in wartime of individual owners of ships to arm them in order to attack the merchant ships of an enemy power when licensed to do so by a letter of marque. In all maritime wars up to the mid-19th century, the merchant shipping of belligerent powers suffered severe losses under the guerre de course, and it was brought to an end by international agreement at the Declaration of Paris in 1856, only the USA refusing to sign the declaration. As a result, US merchant shipping suffered severe losses during the American Civil War (1861–5).
A form of guerre de course was reinstated at the Hague Convention of 1907 when it was agreed among the signatories that merchant ships of a belligerent power could be taken up for war service as armed merchant cruisers. However, this differed from the proper meaning of the term as such ships had to be manned by the navy of the belligerent power and fly its naval ensign. It was not a return to privateering and the letter of marque, which enabled private owners of ships to operate their vessels as warships for private gain. Nevertheless, the result was much the same insofar as commerce-raiding was concerned.
Subjects: Military History — Maritime History.