From the New 'S' class design the Americans developed the T class submarine, a dozen of which were launched in barely 13 months, mostly in 1940. They differed primarily in receiving two extra tubes forward (10 in all) and later substituting a speciallymodified 127-mm (5-in) deck gun for the earlier 101.6-mm (4-in) gun, or 76.2mm (3-in) gun in some cases. This gradual evolutionary process was successful and produced at the right time a submarine with acceptable characteristics for the Pacific war. What was needed was a long endurance and self-sufficiency. Because of the distances involved, patrols were much longer than those in the European theatre and more boats were needed to maintain numbers on station.
Thus the 'Gato' class was an improved T and went into volume production, the first of class, the USS Drum (SS 228), being completed shortly before hostilities commenced. Officially capable of operating down to 91 m (300 ft) they often went deeper. The earlier boats had a large, solid looking sail, similar to those of pre-war designs. These were soon reduced as boats came in for repair but, although the structure could be lowered the very high standards ('shears') demanded by the long periscopes remained a lofty feature. Operating on the surface more than would have been possible in European waters, they began also to accumulate varied outfits of automatic weapons, regular and nonregular, the structures gaining various platforms to support them. Even extra main-calibre deck guns appeared, all in the cause of making the 24 torpedoes aboard last longer.
After 73 boats the hull was secretly improved by the adoption of HT steels and advanced sections, increasing their official limit to 122-m (400-ft) depths. No less than 256 of these were ordered and known as the 'Balao' class, but only 122 were actually completed, a further 10 unfinished hulls being scrapped.
The combined group formed the backbone of the US Navy's wartime submarine strength, achieved much and suffered 29 losses. Post-war, with the example of German developments, many were modernized under the GUPPY programmes, remaining the greater part of the fleet's underwater arm until introduction of the nuclear boats. Many 'went foreign', some still serving.
Specification 'Gato' class Displacement: 1,525 tons surfaced and 2,415 tons submerged Dimensions: length 95.02 m (311.75 ft); beam8.31 m(27.25 ft); draught4.65 m (15,25ft) Propulsion: four diesels delivering 4026.8 kW (5,400 bhp) and four electric motors delivering 2043.2 kW (2,740 hp) to two shafts Speed: 20 kts surfaced and 8.5 kts submerged Endurance: 21316 km (13,245 miles) at 10 kts surfaced and 175 km (109 miles) at 5 kts submerged Armament: one 127-mm (5-in) gun and 10 533-mm (21-in) torpedo tubes (six bow and four stern) for 24 torpedoes Complement: 80