Classification
They may be broadly classified as inshore patrol vessels (IPVs) and offshore patrol vessels (OPVs). They are warships typically smaller in size than a corvette and can include fast attack craft, torpedo boats and missile boats, although some are as large as a frigate. The offshore patrol vessels are usually the smallest ship in a navy's fleet that are large and seaworthy enough to patrol off-shore in the open ocean. In larger militaries, such as in the United States military, offshore patrol vessels usually serve in the coast guard, but many smaller nations navies operate these type of ships.
Read more about this topic: Patrol Vessels