In the global military drawdown that followed World War 2 (1939-1945), the United States Navy (USN) thought well of the idea to destroy most of its collection of Motor Torpedo Boats that played a usually overlooked-yet-crucial role in wrestling control of the Pacific from the Empire of Japan. By the time of the Vietnam War (1955-1975), American authorities were under the belief that modern wars would be settled from behind desks and through vastly superior battlefield technology - indeed the missile was to overtake the "dog fight" in any future air war, rendering close-in guns useless in more modern fighter designs. History would show otherwise.
When the United States began its growing commitment to the Vietnam Conflict, the offshore and riverine aspects of the war required specialized equipment to fight the regional, unconventional war. As such the Navy was forced to look overseas and commissioned twenty wood-hulled, 80-foot long boats from Norway based on their local Tjeld-class MTBs (by Westermoen) that were evolved following Norwegian experiences in World War 2. As North Vietnam lacked conventional naval surface targets for traditional torpedo boats to attack, the torpedo-launching functionality of the new USN boat was removed. The class of twenty was part of the "Nasty-class" and construction spanned from 1962 to 1968. The boats were in commission from 1962 to 1981 and numbered PTF-3 through PTF-22.
The 80-ton vessels exhibited an overall length of 25 meters, a beam of 7.5 meters and a draught of 1.8 meters. The last quality was of particular note for it gave the Nasty boats a very shallow hull profile allowing the series to operate in the shallows of rivers as well as in open waters close to shore. Power was served from a pair of Napier Deltic Turboblown diesel-fueled engines outputting 6,200 horsepower and propelling the fast patrol craft to speeds of 38 knots. A typical crew complement numbered seventeen men and armament was 1 x 40mm Bofors autocannon (at midships facing aft), 2 x 20mm cannons and an 81mm mortar / 0.50 caliber Heavy Machine Gun (HMG) weapon combination mount known as "Piggyback". Additionally the crew could bring their own personal weapons to bear in a given firefight against shore targets.
The USN began its relationship with the Nasty boats through a two-strong order in 1962 (PTF-3 and PTF-4) and these were reinforced through a 1966 follow-on order for fourteen more vessels. Six more were constructed stateside at Annapolis (Maryland) by Trumpy & Sons, one of the few remaining shipbuilders in America who still held experience in building PT boats for the USN back in World War 2.
In service, the PTF series gave a good account of itself and held capabilities lacking in larger warships confined to deep water operations. The PTF served with the "Brown Water Navy" and assisted in various mission types throughout their careers including special forces support and fast assaults on unsuspecting targets. Of the twenty pressed into service, six were lost during the war years. The boats that survived were eventually passed on to the South Vietnamese Navy which operated them until the early 1970s at which point the remaining units were transferred back under USN ownership. From then on, the boats led under-the-radar existences before all were given up for good by the early 1980s - operating costs being a key concern.