Tang-class submarine

Design

Probably the most important innovation of the Tangs, and their primary advantage over contemporary GUPPY conversions, was an increase in test depth from 400 ft (120 m) to 700 ft (210 m), achieved with the same High Tensile Steel (HTS; 42,000 psi (290 MPa) yield strength) as the Balao and Tench classes. This allowed the class to take advantage of deeper ocean conditions to evade sonar, as well as maneuver more safely at moderate depths.

An unsuccessful innovation of the Tang design was the General Motors EMD 16-338 lightweight, compact, high-speed "pancake" engine, rated at 1,000 bhp. Very different from the classic diesel engines that nearly all preceding submarines used, which were laid out with a horizontal crankshaft, this new engine had a vertical crankshaft, and the cylinders were arranged radially like an aircraft engine. Four of these 13+1⁄2-foot-tall (4.1 m), 4-foot-wide (1.2 m), eight-ton engines could be installed in a single engine room, thus deleting an entire compartment from the submarine's design. The goal was to reduce overall length, as testing had shown that shorter submarines were more maneuverable, especially in depth, and had less submerged drag. Four compact Guppy-type 126-cell lead–acid batteries were installed to provide a high sustained submerged speed. The overall design allowed for a 25 kn (46 km/h) top speed and possible future propulsion replacement with a Type XVII U-boat-derived hydrogen peroxide turbine, closed-cycle diesel system, or even a nuclear power plant. However, attempts to develop the first two systems were unsuccessful, and nuclear power plants proved too large to be accommodated in the Tang-class hull.

When the boats went to sea in the early 1950s, the new engines did not work well. Their compact, high-speed design made them difficult to maintain, and they tended to leak oil into their generators. In 1956, the Navy decided to replace the pancake engines with three ten-cylinder Fairbanks-Morse opposed-piston 38D 8-1/8 diesels. These were similar to those of late-war World War II boats, but uprated from 1,350 shp (1,010 kW) to 1,600 shp (1,200 kW) each. To accommodate the larger engines, the boats had to be lengthened some nine feet in the engine room (three additional frames between frames 69 and 70). Accordingly, in 1957 and 1958, the first four Tangs were lengthened, while Gudgeon and Harder, still on the ways, were built to the new length with the new engines. This propulsion plant was used for almost all subsequent US conventional submarines.

The torpedo tubes were also redesigned. The six forward tubes now used air-powered piston ejection pumps, which forced a slug of water through a slide valve behind the torpedo to push it out, rather than the pulse of air used in previous designs. Because this design is somewhat quieter and does not release an air bubble every time a torpedo is fired, it has been used in all subsequent submarine designs throughout the world. The four stern tubes of previous classes were reduced to two shorter, simpler tubes that could not accommodate the longer anti-ship torpedoes and had no capability to actively eject torpedoes. Rather, they were designed for the Mark 27 and planned Mark 37 swim-out torpedoes.