65ft Patrol Boat Mark III “Sea Spectre”, 65PB731 - Specter of the Past

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65ft Patrol Boat Mark III “Sea Spectre”, 65PB731

TL;DR:
Coastal vessel, asymmetrical patrol boat, this prototype of the class has an extra mounting with a twin .50cal.

Overview:
After the end of the Vietnam War, naval requirements for small craft changed drastically, and a new generation of patrol boats were developed by the Norfolk Division of the Naval Ship Engineering Center. The 65ft Patrol Boat Mark III was a successor to the Vietnam-era Swift boats and the unsuccessful CPIC patrol boat prototype. It was an asymmetrical vessel, with the bridge on the starboard side, while the port side had a superfiring platform that allowed for the installation of an autocannon, recoilless rifle, mortar, or twin torpedo tube. Additionally the hull was designed to have a small radar cross-section, though installing weaponry would render that feature useless. The ships had 3 engines, which made the interior space quite cramped, but allowed it greater survivability during engagements. The first Mark IIIs were ordered during Fiscal Year 1973, with 8 built at the Peterson Builders in Wisconsin, and were operated by the Navy SEALs. Additionally 18 more were ordered in FY 75 and 77. None of them had names, being known only by their hull number (65PBYYX, ie 65PB731). The ships in service were rarely fitted with the heavy weaponry it was designed for, making many design choices meant to accommodate them rather pointless. Though a few new small craft weapons were tested on the Mark IIIs: a 40mm Bofors in a new Mod.7 mounting, which was widely adopted, the Norwegian Penguin anti ship missile, which was rejected for being too heavy, and a navalized 25mm Bushmaster, which in 1985 was adopted as a new standard small craft gun. All the Mark IIIs would be discarded by 2000.

The prototype Sea Spectre, hull number 65PB731, differed from the later boats in that it had a gun tub mount above the bridge à la the old Swift boats which mounted a twin .50cal. It was completed and commissioned in ~1974-75, and sometime later had the gun tub removed. Not much else is known about it.

Specifications:

Armament:
1x1 20mm Mk.16
1x2 12.7mm M2
4x1 12.7mm M2
1x1 81mm Mk.2 mortar combined with 1x1 12.7mm M2

Displacement:
31.5 tons standard
41.3 tons full

Length: 19.8m

Beam: 5.5m

Draft: 1.8m

Propulsion: 3 GM 8V-71TI diesel engines, 1800 hp, driving 3 shafts

Speed: 26 knots (48.2 km/h)

Range: 450nmi (at 26 knots)

Crew: 6

Systems:
LN66 navigation radar

Images:





65PB731 moored at the Washington Naval Yard in 1974, likely before commissioning
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A preserved Mark III
Drawings:
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Screenshot (27)
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Sources:
Friedman, N. (1987). Post-Vietnam Small Combatants. In U.S. Small Combatants: Including PT-Boats, Subchasers, and the Brown-Water Navy: An Illustrated Design History (pp. 390–411). Naval Institute Press.
Gardiner, R., Chumbley, S., & Budzbon, P. (1995). USA. In Conway’s All the World’s Fighting Ships 1947-1995 (p. 626). Naval Institute Press.
Moore, C. J. (1974). United States. In Jane’s fighting ships 1974-75 (p. 474). Janes.
Moore, C. J. (1979). United States. In Jane’s fighting ships 1978-79 (p. 684). Janes.
https://www.warboats.org/mk3.htm
https://navysealmuseum.pastperfectonline.com/photo/85F652DC-0C96-42DE-B869-271883460114

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