plant. However, this unusual arrangement was quite cramped, making maintenance and repairs in the aft engine room somewhat difficult. All six of these submarines (and all subsequent U.S. Navy submarines up to the late 1940s) were built to a "partial-double hull" design. In this hull type, the inner pressure resisting hull is wrapped by an outer hydrodynamically smooth hull. The space between these two hulls is used for ballast and fuel tanks. The outer hull smoothly tapers into the pressure hull in the area of the forward and after torpedo room bulkheads, leaving the pressure hull exposed at the extreme ends of the boat. This is actually an advantage as it allows access to the pressure hull in these areas for maintenance. In a full double hull boat, the outer hull completely encompasses the pressure hull and the very narrow ends make it very hard to reach the pressure hull for repairs and maintenance. Ships in class Service history Commissioning and pre-war service Portsmouth proved to be quite efficient in their production methods and they managed to complete and commission both Snapper and Stingray before Electric Boat delivered the lead boat Salmon for commissioning. In fact, all three of the Government built boats of this class beat their commercially built counterparts into service. After commissioning, these boats were very active in the fleet, operating initially with the Atlantic Fleet, conducting exercises in the Caribbean and around both sides of the Panama Canal. They transferred to the Pacific Fleet in late 1939, homeported out of San Diego, commanded by COMSUBPAC Admiral Wilhelm L. Friedell. In October 1941, as war clouds loomed on the horizon, all the Salmons and most other newer available submarines were transferred to the Asiatic Fleet as part of a belated effort to reinforce U.S. and Allied forces in the Philippines. The Japanese occupation of southern Indo-China and the August 1941 American-British-Dutch retaliatory oil embargo had raised international tensions. They operated out of Cavite in Manila Bay until the war commenced. World War II From the very start, the Salmons were in the thick of the fight in the defense of the Philippines. The submarines of the Asiatic Fleet were the primary striking force available to Admiral Thomas C. Hart, the fleet's commander. He was assigned sixteen Salmons or Sargos, the entirety of both classes. The Japanese did not bomb Cavite Navy Yard until 10 December 1941, so