The United States Navy (USN) in World War 2 (1939-1945) relied on three major classes of diesel-electric attack submarine - the Gato-class, the Balao-class and the Tench-class (in order). The Gato-class saw construction begin prior to the American involvement in the conflict in 1940 and seventy-seven boats were completed to the standard. The Balao-class added an impressive one hundred twenty from 1942 until 1946 and proved the most numerous of the USN undersea fleet. The Tench-class was born as an improvement over the previous two classes and numbered twenty-nine boats before the end - some fifty-one were cancelled due to the end of the war.
Culmination of a Years-Long Process
The Tench-class was able to utilize years of wartime data in its design and directly succeeded the Balao-class boats. Production began in earnest in 1944 and would last until 1951. The class was notable for its increased operational range (reaching 16,000 nautical miles from the original 11,000 nm) and hull strength, tested down to 400 feet (surpassing 300ft of earlier boats). In essence, it was the culmination of American boat design during the war that began back with the old P-class ("Porpoise") boats of the mid-1930s.
As with the other two classes, the Tench-class relied on a diesel-electric propulsion scheme which involved marine diesel units for surface running and electric motors tied to battery packs for undersea travel. Four diesels were used for the former and two low-speed direct-drive electrical generators (tied to 2 x 126-cell Sargo battery packs) powered the boat in the latter. This arrangement supplied 5,400 horsepower when surfaced and 2,740 horsepower when submerged and drove a pair of screws at the stern. Surfaced speeds could reach just over 20 knots while undersea travel was limited to 8.75 knots.
The Tench-class improved the machinery some by utilizing a directly-coupled, slow-turning motor and worked better within the confined spaces of the boat's lines. The fuel and ballast areas were also refined for better volume and balance as well as to reduce the risk of flooding and being detected by enemy Anti-Submarine Warfare (ASW) equipment. Diving times were also improved over previous types.
Aboard was a team of eighty-one made up of a mix of officer and enlisted personnel. Onboard stores supplied the crew for up to seventy-five days. Armament was the usual mix of bow- and aft-facing torpedo tubes and deck guns. Ten total 21" torpedo tubes were installed with six at the nose and the remaining four at the tail. Twenty-eight reloads were carried - four extra than the Balao-class due to the revised internal spacing arrangement. On the surface, the boat was armed with the typical 5" (127mm) /25 caliber deck gun on a trainable mounting. This was used against surface targets as needed. Close-in defense was handled by 40mm Bofors and 20mm Oerlikon Anti-Aircraft (AA) weapons - also on trainable mountings. The Tench was outfitted with a Fire Control (FC) computer system as well as radar.
Tench-class and Balao-class
Of relatively all-new design with good endurance and solid firepower, the Tench-class was a force to be reckoned with. Externally they strongly mimicked the lines of the Balao-class and, indeed, the close relationship between the two types was driven home as some of the changes instituted in the Tench design were also brought along in some of the Balao-class boats.
Construction and Activation for Service
USS Tench (SS-417), serving as the lead ship of the group, saw her keel laid down on April 1st, 1944 at the Portsmouth Navy Yard and was launched to sea for evaluation on July 7th of that year. She was commissioned as soon as October 6th, also that same year. Trials were held outside of New London (Connecticut) and Tench took the usual route (by way of the Panama Canal) to the Pacific - heading for the USN base at Pearl Harbor, Hawaii - during December.
Tench would go on to complete three total war patrols due to her late entry into the war. The lateness of the class meant that barely a dozen or so of the boats were actually available for wartime service - many were still in the process of construction, being fitted out or in trials when the war came to a close. However, none would be lost to accident or enemy action as a result.
Her first patrol took her to the East China Sea and the Yellow Sea and ended in April of1945. A refit followed before the second patrol began in May where the boat was active in Japanese homeland waters. Mikamisan Maru was torpedoed and sunk in June and Ryujin Maru followed days later. On June 9th, the freighter Kamishika Maru - Tench's biggest war prize - was sent under. One of her own torpedoes, having entered an uncontrolled circle, threatened the boat but Tench was able to evade before finding peace at Midway.
The third war patrol proved to be her last when she went into action once more - this in late-July. The Empire of Japan surrendered on August 15th, 1945 to officially end World War 2. In March of 1946, Tench was placed in reserve, having journeyed back to the American East Coast (New London). For her relatively short combat service in the Grand Conflict, USS Tench was the recipient of three Battle Stars.
GUPPY Conversion Program
Tench was then modernized through the GUPPY program which made good use of captured German U-boat technology and design philosophy as it related to the ground-breaking Type XXI series (detailed elsewhere on this site). The work made for a more effective attack platform surrounding her performance, particularly when submerged. She was recommissioned for USN service in January of 1950.
In this new guise, Tench operated for twenty more years while undertaking various patrolling actions in Atlantic waters and, later, the Mediterranean Sea - the primary threat of the day was now the Soviet Union. In late-1968, she participated in Operation Silvertower in Atlantic waters as part of a NATO exercise. In October of 1969, she was reclassified with the hull designator of AGSS-417 to mark her as a "General Auxiliary Submarine" amidst the rise of newer and more powerful Navy attack types.
In May of 1970, she was once again placed in reserve status and remained as such until August of 1973 to which point her name was struck from the Naval Register and her hull stripped of its military value. She was then sold for scrap.