Federation Naval Patrol

From Memory Alpha, the free Star Trek reference.

The Federation Naval Patrol was a naval department of the Federation that deals with sea ships that patrol the oceans of Federation worlds, similar to how starships patrol Federation space.

When Tom Paris' father read the novel 20,000 Leagues Under the Sea to him, Tom strongly considered joining the Federation Naval Patrol instead of joining Starfleet. (VOY: "Thirty Days")

Though there was never any further information on screen, it is possible that the Federation Naval Patrol is something like the U.S. Coast Guard, or perhaps an offshoot of the Royal Navy or United States Navy.