Patrol Boat, or Patrol Craft, a small, high-speed naval vessel used for antisubmarine warfare, coastal patrol, harbor defense, and river warfare. The patrol boat classification includes motor torpedo boats, motor gunboats, fast patrol boats (successor to the PT boats [torpedo patrol boats] of World War II), and various kinds of river patrol boats. (Exact designations vary from navy to navy.) Patrol boats are generally about 75 feet (23 m) long, displace less than 100 tons, and carry crews of 11 to 25 men. Many are capable of speeds of better than 40 knots. Hydrofoil patrol boats, which travel on underwater foils (similar to aircraft wings) rather than on their hulls, travel even faster.