letter of mart

The old and the present enumeration in English policies is, "perils of the seas, men of war, fire, enemes, pirates, rovers, thieves, jettisons, letters of mart and countermart, surprisals, takings at sea, arrests, restraints and detainments of all kings, princes, and people, of what nation, condition or quality soever, barratry of the master and mariners, and all other perils."