Letters of Marque : Declarations Against France, Spain, and the United Provinces (HCA 26/33-59) : 1777 - 1783.

Letters of marque were commissions issued during wartime by the Lord High Admiral or Commissioners acting on his behalf, permitting privately owned vessels to be operated as privateers or as armed merchantmen. Before 1739, Orders in Council provided the authority for issuing letters of marque, but after that date an Act of Parliament passed at the beginning of a war was required before letters of marque could be issued. At the time of the American Revolution, the act was passed in 1777 that gave the Lord High Admiral the authority to issue Letters of Marque.

There were two types of private men-of-war. The first was a privateer whose purpose was to seek out and capture enemy vessels. The second was a merchant vessel whose captain had the authority to seize any ships of the enemy he might encounter while engaging in regular trading enterprises. The Letter of Marque provided the evidence that the privateer was acting legitimately on behalf of his government and was not engaging in piracy. The original document was held by the captain of the vessel and a copy was preserved in the records of the High Court of Admiralty. To obtain a letter of marque, an application had to be made in writing to the Lords of the Admiralty, giving a full and detailed description of the vessel, and other details.

During the American Revolution, the Lord High Admiral or his agents issued 7352 letters of marque. Of this number, 2328 were issued against France, 1506 against Spain, and 1233 against the United Provinces. The ports of London, Liverpool, Bristol, the Channel Islands, and ports in the South-East of England, South-West of England and the West of Scotland were major centres of privateering activity against these three nations, while a number of smaller ports also fitted out a considerable number of vessels. Since a Letter of Marque was issued against one particular enemy, privateers often carried several letters of marque, making it possible for them to sail against more than one enemy power.

Prizes were awarded entirely to the captors; the Crown did not receive prize revenue. Letters of marque could remain in effect for the course of hostilities, but a new commission would be issued if there was a change in a vessel's name, the master, ownership, alterations in rigging, additions of guns, change in home port, change in voyage plans, or if the original commission was revoked.