Tench-class submarine

Tench-class submarines were a type of submarines built for the United States Navy (USN) between 1944 and 1951. They were an improvement over the preceding and es, 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 . This improvement was also made on some boats of the previous two classes.Friedman through 1945, pp. 209, 351 Further improvements were made beginning with SS-435, which are sometimes referred to as the Corsair class.

Initial plans called for 80 to be built, and orders eventually were placed for 134 (numbered SS-417 to SS-550), but 105 were cancelled in 1944, 1945, and 1946, when it became apparent that they would not be needed to defeat Japan; a further 12 boats (SS-551 to SS-562) were planned to be ordered in 1945, but orders for these were never placed. Some of these (including numerous units which were cancelled) were allegedly of the Balao design, but official USN publications allot all to the Tench class. The remaining 29 were commissioned between October 1944 () and February 1951 (). The last submarine of the Tench class, as well as the last submarine to have served during World War II, remaining in service with the USN, was the , which was decommissioned on 27 June 1975.

One Tench-class submarine is reportedly still in active service, USS Cutlass (SS-473), which was transferred to the Republic of China Navy in 1973. ROCS Hai Shih (S 791) is expected to remain in service until 2026, 82 years after she was first launched in 1944.

Three Tench-class boats survive as museum ships; USS Torsk (SS-423) and USS Requin (SS-481) are in the United States, and USS Thornback (SS-418), renamed TCG Uluçalireis (S 338), is in Turkey.

Design

The as-built diesel-electric propulsion layout was the same as the last few boats of the 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 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 because the gearing was an element prone to shock damage from depth charges.Johnston, pp. 11 Two 126-cell -type lead-acid batteries provided submerged power to the electric motors.

A design weakness of earlier classes solved by the Tench redesign was having the ballast tank vent riser pipes pass through the interior of the boat in the forward and after torpedo rooms. These pipes allowed #1 and #7 main ballast tanks (MBTs) (located in the single-hull sections of the boat) to vent air during diving, which allowed water to flood into them from below. The tops of these MBTs formed the walking deck in the interior of both rooms, thus the normal location of the vent valves (the top of the tank) could not be used. The riser pipes allowed the MBTs to vent, but when they 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 MBTs. The #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 MBTs. This move eliminated the riser pipes completely. The #7 MBT, after stability and buoyancy calculations were run, was found to be redundant and was converted to a variable fuel oil/ballast tank, increasing the class's surfaced range. These changes forced a rearrangement of the associated piping runs and locations of many of the other tanks. Being almost entirely internal, 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). Another difference was the elimination of small bulges around the motor room that previously accommodated the reduction gears.

A significant benefit of the tank rearrangement was that these boats could carry two additional torpedoes for the lower bow tubes in the forward torpedo room, giving a total of 26 torpedoes carried. Later, this was increased again with two additional torpedoes for the bottom stern tubes in the aft torpedo room, for a total of 28 torpedoes carried. Submarine crews had been asking for more torpedoes, but this could not be accommodated in the previous classes, as the vent risers restricted the available space.Johnston, pp.11–12

Torpedoes At the beginning of World War II, the standard torpedo for US fleet submarines was the 21-inch Mark 14 torpedo. As the war progressed, the USN introduced the electric, wakeless Mark 18 Torpedo and the Mark 23 torpedo, a simplified, high-speed-only version of the Mark 14. Additionally, a small, 19-inch swim-out, acoustic-homing Mark 27 torpedo supplemented the armament in fleet boats for defense against escorts. Near the end of the war, the offensive Mark 28 acoustic-homing torpedo was introduced. Well after the war, the Mark 37 Torpedo was introduced.http://navweaps.com/Weapons/WTUS_Main.php NavWeaps.com Weapons-Torpedoes-United States of America

Deck guns 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 boats were armed with a /25 caliber gun, and some boats had two of these. Additional antiaircraft guns included single 40mm Bofors and twin 20mm Oerlikon mounts, usually one of each.Friedman through 1945, pp. 214-219

Mine armament Like the previous Tambor/Gar, Gato, and Balao classes, the Tench class could substitute mines in place of torpedoes. For the Mk 10- and Mk 12-type mines used in World War II, each torpedo could be replaced by as many as two mines, giving the submarine a true maximum capacity of 56 mines. However, doctrine was to retain at least four torpedoes on mine-laying missions, which further limits the capacity. The maximum is often stated as 40 mines in various publications because the authors simply used previous limitations of the Gato and Balao classes and included the four-torpedo doctrine. In practice during the war, submarines went out with at least eight torpedoes, and the largest minefields laid were 32 mines. After the war, the Mk 49 mine replaced the Mk 12, while the larger Mk 27 mine was also carried, which only allowed one mine replacing one torpedo. This mine could be set to travel 1000 to 5000 yards from the boat before deploying (not to be confused with the Mk 27 homing torpedo).ORD696 Operational Characteristics of U.S. Naval Mineshttp://navweaps.com/Weapons/WAMUS_Mines.php NavWeaps.com Weapons-ASW and Mines-United States of America-Mines

Boats in class

In all, 29 of these boats were built during and after World War II, commissioned from October 1944 through February 1951, with 11 postwar commissions.Bauer and Roberts, pp. 280-282This includes , commissioned on 13 August 1945, the day hostilities ceased, as postwar. None of this class was lost in World War II.

With one exception, these boats were all built at government-owned shipyards - Portsmouth Naval Shipyard and Boston Navy Yard. Two boats, USS Wahoo (SS-516) and an unnamed boat designated SS-517, were laid down at Mare Island Navy Yard but canceled and broken up prior to completion. With the end of the war obviously near and due to a large construction backlog of Balao-class boats, the Electric Boat Company was only awarded contracts for three Tench-class boats, only one of which, , was completed. Electric Boat's follow-on yard, the Manitowoc Shipbuilding Company of Manitowoc, Wisconsin, worked through its contracts for Balaos and was not awarded any Tench contracts. The Cramp Shipbuilding Company of Philadelphia, struggling with workforce problems and supply issues with its Balaos, was also not awarded any contracts.Johnston, pp. 13–14

Cancellations

In total, 125 U.S. submarines were cancelled during World War II; all but three between 29 July 1944 and 12 August 1945. The three exceptions were USS Wahoo (SS-516), , and , cancelled on 7 January 1946. References vary considerably as to how many of these were Balao- and how many were Tench-class boats. Some references simply state all submarines numbered from SS-416 onwards were of the Tench class; the Dictionary of American Naval Fighting Ships (Volume 1, published in 1959 by the US Navy Department) confirms this; however, and were allegedly completed as Balaos.Silverstone, pp. 203–204; Gardiner and Chesneau, pp. 145–147. There were also 10 earlier cancelled Balaos, SS-353 to SS-360, SS-379 and SS-380. The Register of Ships of the U. S. Navy differs, considering every submarine not specifically ordered as a Tench to be a Balao, and further projecting SS-551 to SS-562 as a future class. This yields 62 cancelled Balao- , 51 cancelled Tench-, and 12 cancelled "SS-551"-class boats. Two of the cancelled Tench-class boats, Unicorn and Walrus, were launched incomplete in 1946 and never commissioned, but listed with the reserve fleet until struck in 1958 and scrapped in 1959. The cancelled hull numbers, including those launched incomplete, were SS-353 to SS-360 (Balao), 379 and 380 (Balao), 427–434 (Tench or Balao), 436–437 (Tench), 438–474 (Tench or Balao), 491–521 (Tench), 526-529 (Tench), 530–536 (Tench or Balao), 537-550 (Tench), and 551-562 (Tench or a possible future class, but for which no orders were actually placed).

Service

Ten of the 29 Tench-class submarines completed were 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-total 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.

After the war, 24 of the 29 Tench-class boats 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 remained active in Taiwan's Republic of China Navy as Hai Shih as of July 2021, the last of the class in service with any navy.

Naval Reserve trainer

Interested in maintaining a ready pool of trained reservists, the Navy assigned at least 58 submarines from 1946 to 1971 to various coastal and inland ports (even in Great Lakes ports such as Cleveland, Detroit, and Chicago), where they served as training platforms during the reservists' weekend drills. At least three Tench-class boats served in this capacity. In this role, the boats were rendered incapable of diving and had their propellers removed. They were used strictly as pierside trainers. These were in commission but classed as "in commission in reserve", thus some were decommissioned and recommissioned on the same day to reflect the change in status.Friedman 1995, p. 285Reserve Training Boats at SubmarineSailor.comFriedman since 1945, pp. 228–231

Foreign service