The LSSL began life as the smallest ocean-going landing craft, the LCI (landing craft, infantry). Originally called the Landing Craft Support (Large) Mark 3, the LSSL used the same hull of the LCI, but was configured for gunfire support of the landing beaches. The U.S. built 130 of these “mighty midgets” during the war.
LSSL [aka LCS(L) Mk 3] specifications (1945):
Displacement - 250 tons (light), 387 tons (full load)
Length - 158’ 6” overall
Beam - 23’ 3”
Draft loaded - 4’ 9” forward, 6’ 6” aft
Speed - 16.5kts max at 650 shaft rpm, 14.5kts at 585 shaft rpm
Armor - 10-lb STS splinter shield to gun mounts, pilot house and conning tower
Complement - 6 Officers, 65 Enlisted
Propulsion - 8 GM diesels, 4 per shaft, BHP 1,600, twin variable pitch propellers
Endurance - 5,500 miles at 12kts at 45” pitch (350 tons displacement)
Fuel/Stores - 76 tons fuel oil, 10 tons fresh water, 6 tons lubrication oil, 8 tons provisions and stores at full load
Fresh Water Capacity - distill up to 1,000 gals. per day
Armament - bow gun, one single 3”/50 DP (dual purpose) gun mount
two twin 40mm AA gun mounts
four single 20mm AA gun mounts
four .50 cal machine guns
ten MK7 rocket launchers
The PT boat started the war as a torpedo boat to attack large vessels, but turned into a gunboat as the war progressed. The PT boat was not ocean-going with a range like the LSSL and it burned aviation grade gasoline. It was very heavily armed for its size and weight.
PT-596 specifications (1945):
Displacement - 56 tons
Length - 80’
Beam - 20’ 8”
Draft - 5’
Speed - 41 kts.
Complement - 17
Armament - One 37mm mount, one 40mm mount, one 20mm mount, two Mk 50 rocket launchers, four Mk 13 aircraft (22.4-inch) torpedoes and two twin .50 cal. machine guns
Propulsion - Three 1,500 shp Packard W-14 M2500 gasoline engines, three shafts.
Endurance - 6.3 hours at 40 knots on 3 engines, 474 gallons per hour; 10.3 hours at 2,000 rpm (35 knots), 292 gph, 518 miles max.
The impression I get is that the surface navy is focused on the aircraft carrier, and supporting the carriers. The job of the destroyers, frigates, and cruisers is to operate as an anti-submarine/anti-air/anti-missile shield for the carrier.