A patrol boat (also referred to as a patrol craft, patrol ship or patrol vessel) is a relatively small naval vessel generally designed for coastal defence, border protection, immigration law-enforcement, search and rescue duties. There have been many designs for patrol boats. They may be operated by a nation’s navy, coast guard, police force or customs and may be intended for marine (“blue water”) or estuarine (“green water”) or river (“brown water”) environments. They are commonly found engaged in various border protection roles, including anti-smuggling, anti-piracy, fisheries patrols, and immigration law enforcement. They are also often called upon to participate in rescue operations.
They may be broadly classified as inshore patrol vessels (IPVs) or 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 is large and seaworthy enough to patrol off-shore in the open ocean. Smaller inshore patrol vessels also known as coastal patrol craft or coastal patrol boats. Riverine patrol craft are used for patrol river area. 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.