East Indiamen warrants
A register of warrants granted by the Crown to East Indiamen are held in The National Archives, record series HO 118/1 ('Special commissions: for seizing pirates [to commanders of East India Company's ships proceeding to India and the Far East]'). Jenny Fawcett has indexed these and they are available on the FIBIS database.
About the series
The royal warrants grant the master of each listed EIC ship license to 'apprehend, seize or secure all Pyrates, Free Booters and Sea Rovers, together with Their Ships and Vessels' that they encounter on their routes to India and the Far East. The register runs from 1768 to 1826, lists 315 vessels and for each notes the ship’s name, commander, its burthen and the number of men and guns on board.