During the Revolutionary War period, the colonies (and then the U.S. Congress) used to issue so-called letters of marque to private ships to help fight enemies, like the British. This privateering was an important part of the government’s war-fighting strategy, since its Navy was not particularly big or powerful at the time (the framers were pretty wary of keeping standing armies and navies). The Constitution provides that Congress has the power to issue letters of marque, although the United States hasn’t issued one of these things since the War of 1812.
Apparently, however, the Republic of Texas issued a couple in the 1830s. Here is a press release from the Texas General Land Office describing some newly found documents about the Texas Navy (it had 4 ships, which were all destroyed during the Revolution against Mexico) and at least one privateer from Texas who sailed under a letter of marque. Pretty interesting stuff.
By the way, did you know that Nebraska has a Navy? I wonder if they’ve ever issued any letters of marque.