Known as the New 'S' class because the early units confusingly took pendants of the Old 'S' class boats still in service, 16 boats were built in two very similar groups. Their design was based closely upon that of the preceding 1,320-ton 'P' class, but differed particularly in having a deeper stern to accommodate an increase in the after torpedo tube complement from two to four. The 'P' and 'S' class boats were the first all-welded submarines in the US Navy and, though techniques were still being developed, the workmanship was sound, as evinced by the survival of the USS Salmon (SS 182), lead boat of the New 'S' class Group 1, which was severely depth charged in October 1944 by four Japanese escorts after torpedoing a tanker off Kyushu. The combination of concussion and the effects of overpressures through being driven far below design depth left the hull dished between frames, but the boat made it home. Irreparable, she was eventually scrapped. The double hull of the American boats was a protective feature, provided that the ballast and fuel tanks within retained an ullage space over the liquid contents.
Composite propulsion systems were fitted in some, arrangements whereby the two forward diesels drove generators directly and the two after units were geared to the shafts, the gearing being shared also by two propulsion motors on each shaft. Though complex, the arrangement proved satisfactory.
Twelve reload torpedoes were located within the pressure hull and four more in external stowage in the casing, an arrangement vulnerable to the effects of depth charge attack. Two mines could be carried for each internal torpedo and laid through the tubes. Originally a 76.2-mm (3-in) gun was fitted, but this was changed to a 101.6mm (4-in) weapon in the majority of boats. Wartime modifications saw the bulky 'sails' cut down to a profile similar to that of later classes.
The New 'S' class Group 2 included the USSSgualus (SS 192), which foundered through an induction valve failure while on trials in May 1939, Salvaged and refitted, she survived the war as the USS Sailn'sh. The USS Swordfish (SS 193) was credited with the first Japanese merchantman sunk, a week after the outbreak of war.
Specification New 'S' class ('Salmon' group) Displacement: 1,440 tons surfaced and 2,200 tons submerged Dimensions: length 93.88 m (308.0 ft); beam 7.98 m (26,17 ft); draught 4.34 m (14.25ft) Propulsion: composite drive with four diesels delivering 4101.4 kW (5,500 bhp) and four electric motors delivering 1983.6 kW (2,660 hp) to two shafts Speed: 21 kts surfaced and 9 kts submerged Endurance: 18532 km (11,515 miles) at 10 kts surfaced and 158 km (98 miles) at 5 kts submerged Armament: one 76.2-mm (3-in) gun (later upgraded to one 101.6-mm/4-in gun in most units) and eight 533-mm (21-in) torpedo tubes (four bow and four stern) for 24 (later 20) torpedoes Complement: 75