Balao Class, U.S. Submarines

Naval Historical Center #NH 98043

ONI 222

Specifications:

The Balaos were completed in 1943-45 and were essentially Gatos with strengthened hulls. This allowed them to dive deeper, which was tactically important when evading Japanese depth charge attacks. The boats so resembled the Gatos In every other respect that the Navy was able to conceal the design change throughout the duration of the war. The Japanese, who apparently were aware of the standard 250' (76 meter) design depth of the American prewar submarine classes, were unaware of the greater diving depth of the wartime submarine classes until this information was leaked by a Congressman back from a junket in the Pacific.

The increase in hull thickness without any other significant design changes was possible because the Gatos used a considerable amount of lead ballast. Increasing the hull thickness provided the extra weight needed to eliminate the expensive lead ballast while increasing the dive depth.

The hull plate on the Balaos was increased in thickness from 0.5625" (14.3mm) to 0.875" (22.2mm) and the plate material was upgraded from mild steel to high-tensile steel (HTS). It was calculated that this would increase the crush depth to 900 feet (270m) but other components, such as propeller shaft glands and the trim pump, could not be redesigned quickly to take the higher pressure and the maximum design operating depth was set to 400 feet (120m). As it turned out, the composition of high-tensile steel was changed from a chrome-vanadium steel alloy to a slightly weaker titanium-manganese steel alloy whose manufacture fewer scarce resources, so the large safety factor was beneficial. A Gould centrifugal pump was adopted in 1944 that could operate at 600 feet (180m) depth or more, and the refitted Balaos were thereafter able to more fully exploit their thick skins.

A particularly important improvement to the boats was the development of a slow, heavy-duty motor that replaced the older high-speed motors and reduction gears. Besides increasing reliability and saving space, the new motors eliminated the characteristic loud whine produced by the reduction gear. This was ready in time to be installed on new boats commissioned from July 1944 onwards. Another improvement was elimination of phenolic insulating materials, which burned when exposed to flame or electrical arcs (as from short circuits) to produce toxic smoke. The replacement, melamine insulation, has enough nitrogen in its chemical makeup to produce inert nitrogen gas when charred, which suppressed burning.

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References

Alden (1979)

Blair (1975)

DANFS

Friedman (1995)

Worth (2001)

The Pacific War Online Encyclopedia © 2007, 2009, 2012-2013, 2015 by Kent G. Budge. Index

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