noun
patrol boat; patrol vessel
Typically refers to a Japan Coast Guard patrol boat used for maritime surveillance, search and rescue, and law enforcement.
巡視船が領海をパトロールしている。
A patrol boat is patrolling the territorial waters.
警備艇 is a more general term for a security or guard boat, not limited to coast guard use.
Compound of 巡視 (patrol, inspection) and 船 (ship, boat).