About the U.S. Navy PBR31 Mk.II "Pibber"
Knowing that patrolling coastal and river waterways during a conflict in Vietnam was going to be extremely hazardous, the U.S. Navy searched for a boat design that could be quickly produced and employed. One chosen was a fiberglass-hulled pleasure craft built by Modutec Marine in Seattle Washington.

The Patrol Boat, River or PBR as it was known militarily, became one of the most successful weapons systems used in Southeast Asia. It was 31' 11" long ; 11; 7" wide, and 9'9" high above the waterline. It displaced 8 3/4 tons loaded drawing two feet of water. It's crew of four was armed with a pair of .50 cal gun or grenade launcher mounted on a tripod in the fantail, plus a single M-60 on a pipe mount bolted to one of the amidships splinter shields. It was powered by two turbocharged Detroit Diesel 205 HP, V-6 marine engines, driving a pair of Jaccuzzi 14JY water jetdrives. The engines were located underneath the aft decking, and the boat was steered by two movable nozzles below the water line, mounted on the rear transom. The water intakes were located on the hull bottom. It had a top speed in excess of 25 knots. Surface radar and two-way radio equipment provided communication and maneuvering safety.