Pennsylvania Class Battleship - Underwater Protection

Underwater Protection

The designers had noted the increasing size, range and explosive power of torpedoes as torpedo designs improved. Recent innovations now had brought torpedo designs with ranges up to 10,000 yards. In addition the design of the Davis torpedo was a concern. The Davis torpedo delivered an 8-inch (203 mm) artillery shell in a gun barrel housed within a torpedo. As a result a series of caissons were built (actual sections of the hull as they were proposed for construction) and tested with both external armor and internal armor. The Davis gun could cause damage but the answer to the Davis gun was external armor, the external armor however greatly increased the amount of damage caused by a conventional torpedo. As a result of the caisson tests the Pennsylvania-class battleships were designed with a 4 layer system of thin plating, air space, thin plate, oil space, thin plate, air space, followed with an armored layer 9.5 feet (2.9 m) inboard. This allowed the explosion to dissipate in the air space and deform the liquid loaded back plate. This section withstood the explosion of 300 pounds (140 kg) of dynamite placed against the hull of the caisson.This was considerably in advance of any navy at the time.