Tench-class submarine

Tench-class submarines were a type of submarine built for the United States Navy (USN) between 1944 and 1951. They were an evolutionary improvement over the Gato and Balao classes, only about 35 to 40 tons larger, but more strongly built and with a slightly improved internal layout. One of the ballast tanks was converted to carry fuel, increasing range from 11,000 nautical miles (20,000 km) to 16,000 nautical miles (30,000 km). This improvement was also made on some boats of the previous two classes. Further improvements were made beginning with SS-435, which are sometimes referred to as the Corsair class. Initial plans called for 84 to be built, but 55 were cancelled in 1944 and 1945 when it became apparent that they would not be needed to defeat Japan. The remaining 29 were commissioned between October 1944 (Tench) and February 1951 (Grenadier).

Tench-class submarine
Class Ship
Type Submarine
Manufacturer HMNB Portsmouth
Origin Italy
Country Name Origin Year
Italy 1944
Country Name Operational Year Retirement Year
Bolivia 1944 1975 View
Brazil 1944 1975 View
Canada 1944 1975 View
China 1944 1975 View
Greece 1944 1975 View
Italy 1944 1975 View
Pakistan 1944 1975 View
Peru 1944 1975 View
Turkey (Ottoman Empire) 1944 1975 View
United States of America 1944 1975 View
ManufacturerName Production From Production To Quantity
HMNB Portsmouth View
General Dynamics Electric Boat View
Boston Navy Yard View

The as-built diesel-electric propulsion layout was the same as the last few Balao class, with four Fairbanks-Morse or General Motors Cleveland Division two-stroke diesel engines supplying two low-speed double-armature direct-drive electric motors to drive two shafts. All except Corsair received the Fairbanks-Morse 38D 8-1/8 engine with 10 cylinders; Corsair had GM 16-278A engines. The direct-drive electric motors were much quieter than the reduction gear arrangement of previous classes, and they made the drive train much more reliable due to the fact that the gearing was an element prone to shock damage from depth charges.Two 126-cell Sargo-type lead-acid batteries provided submerged power to the electric motors.

A design weakness of earlier classes solved by the Tench re-design were the ballast tank vent riser pipes that passed through the interior of the boat in the forward and after torpedo rooms. These pipes allowed #1 and #7 Main Ballast Tanks (MBT) (located in the single hull sections of the boat) to vent air during diving and allowing water to flood into them from below. The tops of these tanks formed the walking deck in the interior of both rooms and thus the normal location of the vent valves (the top of the tank) could not be used. The riser pipes allowed the tanks to vent but when the tanks were full these pipes contained water at full submergence pressure inside the torpedo rooms. If these pipes ruptured during depth charge attack, catastrophic flooding would occur. Solving this problem initially proved quite difficult, but ultimately required the complete rearrangement of the ballast tanks. #1 MBT was moved to a location forward of the end of the pressure hull, thus allowing it to vent directly into the superstructure like the rest of the MBT's. This move eliminated the riser pipes completely. #7 MBT, after stability and buoyancy calculations were run was found to be redundant and was converted to a variable fuel oil tank as mentioned above. These changes forced the rearrangement of the associated piping runs and the location of many of the other tanks. Remarkably, these changes resulted in a boat that was visually almost indistinguishable from the earlier Balao class, with the exception of a sharper angle (or knuckle) at the lower corner of the bow (only visible when the boat was drydocked).

A side benefit of the tank rearrangement was that these boats could carry four additional torpedoes in the forward torpedo room, for a total of 28. This was a change that had been asked for by submarine crews much earlier, but could not be accommodated in the earlier designs due to the lack of space in the torpedo rooms.

Many targets in the Pacific War were sampans or otherwise not worth a torpedo, so the deck gun was an important weapon. Due to war experience, most Tench class were armed with a 5 inch (127 mm)/25 caliber gun, and some boats had two of these. Additional anti-aircraft guns included single 40mm Bofors and twin 20mm Oerlikon mounts, usually one of each.

Ships in Class

  • USS Tench (SS-417)
  • USS Thornback (SS-418)
  • USS Tigrone (SS-419)
  • USS Tirante (SS-420)
  • USS Trutta (SS-421)
  • USS Toro (SS-422)
  • USS Torsk (SS-423)
  • USS Quillback (SS-424)
  • USS Corsair (SS-435)
  • USS Unicorn (SS-436)
  • USS Walrus (SS-437)
  • USS Argonaut (SS-475)
  • USS Runner (SS-476)
  • USS Conger (SS-477)
  • USS Cutlass (SS-478)
  • PNS Ghazi
  • USS Medregal (SS-480)
  • USS Requin (SS-481)
  • USS Irex (SS-482)
  • USS Sea Leopard (SS-483)
  • USS Odax (SS-484)
  • USS Sirago (SS-485)
  • USS Pomodon (SS-486)
  • USS Remora (SS-487)
  • USS Sarda (SS-488)
  • USS Spinax (SS-489)
  • USS Volador (SS-490)
  • USS Pompano (SS-491)
  • USS Grayling (SS-492)
  • USS Needlefish (SS-493)
  • USS Sculpin (SS-494)
  • USS Amberjack (SS-522)
  • USS Grampus (SS-523)
  • USS Pickerel (SS-524)
  • USS Grenadier (SS-525)
  • USS Dorado (SS-526)
  • USS Comber (SS-527)
  • USS Sea Panther (SS-528)
  • USS Tiburon (SS-529)


Ten of the 29 Tench-class submarines were completed in time to conduct war patrols in World War II, entering service beginning in late 1944. They finished what the previous classes had largely accomplished: the near-destruction of the Japanese merchant fleet. Another significant contribution was the rescue of downed aviators near Okinawa and Japan. Two additional boats (Cutlass and Diablo) entered Japanese waters on their first war patrols immediately after the 13 August 1945 cease-fire. Construction on the last four of the class was suspended, and they were completed 1948-1951. Postwar, 24 of the 29 Tenches were modernized under the Fleet Snorkel and Greater Underwater Propulsion Power (GUPPY) programs, with most continuing in US service into the early 1970s. Fourteen were transferred to foreign navies for years of additional service, and the former USS Cutlass (SS-478) remains active in Taiwan's Republic of China Navy as Hai Shih.

Class overview
Builders: Portsmouth Naval Shipyard,Electric Boat Company, Boston Navy Yard
Operators:  United States Navy
 Turkish Navy
 Hellenic Navy
 Peruvian Navy
 Pakistan Navy
 Republic of China Navy
 Royal Canadian Navy
 Marina Militare
 Brazilian Navy
 Bolivarian Armada of Venezuela
Preceded by: Balao class
Succeeded by: Barracuda class
Subclasses: Corsair class
Built: 1944–1951
In commission: 1944–1975
Completed: 29
Cancelled: 55
Active: 1
Lost: 1
Retired: 27
Preserved: 3
General characteristics
Type: Diesel-electric submarine
Displacement: 1,570 tons (1,595 t) surfaced
2,416–2,429 tons (2,455–2468 t) submerged
Length: 311 ft 8 in – 311 ft 9 in (95.0 m)
Beam: 27 ft 3 in – 27 ft 4 in (8.3 m)
Draft: 17 ft (5.2 m) maximum
Propulsion: 4 × diesel engines driving electrical generators (Fairbanks-Morse orGeneral Motors (Corsair only))
2 × 126-cell Sargo batteries
2 × low-speed direct drive electric motors (Elliott Company, General Electric, or Westinghouse)
two propellers
5,400 shp (4,000 kW) surfaced
2,740 shp (2,040 kW) submerged
Speed: 20.25 knots (38 km/h) surfaced
8.75 knots (16 km/h) submerged
Range: 16,000 nautical miles (30,000 km) surfaced at 10 knots (19 km/h)
Endurance: 48 hours at 2 knots (3.7 km/h) submerged
75 days on patrol
Test depth: 400 ft (120 m)
Complement: 10 officers, 71 enlisted
Armament: 10 × 21-inch (533 mm) torpedotubes
 (six forward, four aft)
 28 torpedoes
1 × 5-inch (127 mm) / 25 caliber deck gun
Bofors 40 mm and Oerlikon 20 mmcannon

End notes