Salmon Class Submarine - Design

Design

Authorized under the Fiscal Year 1936 provision of the Vinson-Trammel Act, two distinct, but very similar, designs were developed, to be built by three different constructors. The Electric Boat Company of Groton, Connecticut designed and built Salmon, Seal, and Skipjack (SS-182 to 184). The Navy's lead submarine design entity, the Portsmouth Naval Shipyard of Kittery, Maine submitted a design for the Government group, which became Snapper and Stingray (SS-185 & 186). Using the Portsmouth plans and acting as a follow yard, the Mare Island Naval Shipyard of Vallejo, California built Sturgeon (SS-187). The two designs differed in minor details such as the locations of the access hatches for the forward engine room and crew's quarters, the shape of the horizontal conning tower cylinder, and, most significantly, the closure of the main induction valve. This difference led to casualties in Snapper and Sturgeon, and to the loss of Squalus. Larger than the design of the Porpoise-class, the conning tower installed by Electric Boat had two concave spherical ends, The Portsmouth design had a concave end aft and a convex one forward. Portsmouth and Mare Island ran into production difficulties with their conning towers, discovering cracks that caused the cylinder to fail the required pressure test. The problem was successfully fixed, but the experience caused the government yards to adopt the double concave design for the next several years.

Externally, there were minor differences in the shape of the upper edge of the aft end of the conning tower fairwater. The Electric Boat design had a gradual downward taper to this bulwark, the Government design was slightly higher and straighter. Also, as built the Electric Boat trio had two 34 foot periscopes. This resulted in a fairly small periscope shear support structure above the fairwater. The three Government boats had one 34 foot and one 40 foot periscope and this necessitated a taller shear and support stanchions.

The Electric Boat-built Porpoises had been built to an all-welded design. Conservative engineers and shipfitters at the Government yards stuck with tried and true riveting. Electric Boat's method proved superior, providing a stronger and tighter boat, as well as preventing leakage of fuel oil tanks after depth charge attacks. Finally convinced of the efficacy of Electric Boat's innovation, Government yards finally converted wholesale to welding for their three Salmons and the Navy was entirely happy with the results.

The six boats of this class were straight forward derivations of the later boats of the preceding Porpoise class. Although considered to be successful in most respects, valuable lessons had been learned from the Porpoises and operating experience showed the need to expand the operating envelope. The Salmons were longer, heavier, and faster versions with a better internal arrangement and a heavier armament. Two additional torpedo tubes were added to the aft torpedo room, for a total of four forward and four aft. Some submariners wanted six tubes forward, but design philosophy and tactics of the day did not yet support this. However, in an effort to increase the number of torpedoes carried, four non-firing torpedo stowage tubes were installed in the superstructure below the main deck, stacked vertically, two each on either side of the conning tower. In order to access the weapons in these tubes, the boat had to surface and remove a portion of the decking on either side of the deck gun. Small boats stowed there for running sailors ashore for liberty were removed and set in the water. The weapons were extracted from the tubes one by one and winched up to the main deck. They were then placed on a raised loading skid and carefully lowered on an angle through a hatch into the forward torpedo room. This whole process took several hours to complete. The impracticality of spending several hours on the surface in enemy waters moving torpedoes below was lost on the designers. War experience led to the removal of these tubes during the boats' first wartime overhauls.

Two different main (diesel) engine types were installed in these boats during construction. The Government boats received a new model GM-Winton 16-248 V16. Steady development work by GM-Winton had largely corrected earlier problems and this engine proved to be fairly reliable and rugged. The three Electric Boat units received a nine-cylinder version of the Hooven-Owens-Rentschler (HOR) double acting engine. This was based on a successful steam engine design. Having a power stroke in both directions of the piston, this engine promised nearly twice the horsepower in a size similar to a conventional in-line or V-type engine. Unfortunately, HOR encountered severe design and manufacturing difficulties converting the concept to internal combustion. They vibrated excessively due to imbalances in the combustion chambers. This broke engine mounts and caused difficulties in the drive train. Improper manufacturing of the gearing resulted in broken gear teeth. Reluctant to give up on the promise of the engine, the Navy coddled the HORs along until after the Pacific War began, when increased funding and operational needs caused these engines to be replaced with GM-Winton 16-278As during the boat's first wartime overhauls.

Serious problems were encountered with the Porpoise-class all-electric drive. This drove the decision to radically alter the propulsion plant. The Salmons were fitted with the so-called "composite drive". In this arrangement, two main engines in the forward engine room drove generators in the fashion set by the Porpoises. In the after engine room, two side-by-side engines were clutched to reduction gears which sat forward of the engines. The propeller shafts led aft from from each of the reduction gears, and were sited outboard of the engines. Two electric motors were mounted outboard of each shaft, connected directly to the reduction gears. For surfaced operation the engines were clutched in to the reduction gears and drove the propellers directly, with the generator engines providing additional voltage to the motors. For submerged operation, the direct drive engines were declutched from the reduction gears and the motors drove the shafts with electricity supplied by the batteries. Although proven to be satisfactory in operation, 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.