Coastal vessel, USS Tucumcari, but fitted with 6 20mm guns during the living advertisement phase of its career. Can be a modification or something.
In 1970, USS Flagstaff and Tucumcari returned from their tour of duty in Vietnam. Afterwards, the two PGHs’ paths would diverge. Flagstaff became a test ship, while Tucumcari was deployed to Europe. Its rear mortar was replaced with an Emerson Electric twin turret, which could be remote controlled, and the twin 12.7mm MGs replaced with twin 20mm autocannons. It was used as a demonstrator for the NATO PHM program, visiting many ports and conducting exercises. As a demonstrator it was relatively successful, with Italy’s Sparviero-class hydrofoils being based on Tucumcari’s design. The twin turret was removed halfway through 1971, and it returned to the US at the end of that year, but continued to be used as demonstrator, mainly for the US Coast Guard. Unfortunately in late 1972, while doing nighttime training, Tucumcari ran aground on a coral reef near Puerto Rico, and was damaged so severely it was written off. The salvaged hull was sent to the Naval Ship Research and Development Center to be used in structural and firing tests. Ultimately Tucumcari’s design elements would prove more appealing to the Navy than Flagstaff, and its builder Boeing would be awarded the contract for the Pegasus-class Hydrofoils.
The Emerson Electric EX-73 mount was originally developed for the ATC Mk.2, but was tested aboard Tucumcari. It could be fitted with 20mm autocannons, .50cal MGs, or 30mm grenade launchers, and could be remote controlled. In the 20mm configuration, each gun was fed from a 250 round magazine.
1x1 40mm Bofors L/60 Mk.3
1x2 20mm Mk.16 in Emerlec EX-73 mount (+65° and -15° elevation, 30° elevation speed and 60° rotation speed, 250 round magazines)
2x2 20mm Mk.16
58 tons full
Draft: 1.3m (foils up) or 4.2m (foils down)
Propulsion: 1 Bristol Proteus gas turbine + 1 GM 6V-53 diesel engine, 3100 + 150 hp, driving 2 waterjets + 1 shaft
Speed: 50 knots (92.6 km/h)
Friedman, N. (1987). Motor Gunboats and PTFs. In U.S. Small Combatants: Including PT-Boats, Subchasers, and the Brown-Water Navy: An Illustrated Design History (pp. 257-263). Naval Institute Press.
Sayers, K. (2021). Patrol Gunboat-Hydrofoils. In U.S. Navy Patrol Vessels (pp. 235-240). McFarland.