Fleet Submarine Defined
by James Christley
Submarine design from the earliest days of the century had been divided by the need for the ship to be available to defend the shores and harbors of the owning country which allowed for a small short ranging boat and the so called fleet submarine which could move with the main battle fleet and extend its reach and threat profile by attacking an enemy fleet as the two closed. The engineering tradeoffs that formed the basis of the design of the submarine were most difficult. The speed requirement of nearly thirty knots demanded a large propulsion plant and drove the size of the hull and its requisite displacement upward. But coupled with this was the limiting amount of propulsion power available in the battery and motors of the day which defined the available submerged speed and range.
The standard model propulsion plant in the early submarines of the interwar period was one in which surfaced power was provided by two diesel engines, each driving one propeller shaft. Also mounted on this shaft was an electric dynamo. If the engine was driving the shaft, the dynamo could be used an electric generator to charge the lead acid storage batteries. When the submarine submerged and was no longer able to provide the vast quantities of air to the diesel, the engine was stopped and a clutch provided between the engine and the dynamo was opened. Then the dynamo was the operated as an electric motor using the stored electrical energy of the battery to drive the propeller shaft.
While navies had experimented with other forms of propulsion including steam and compressed air, none had developed a system that seemed to be more effective than the direct diesel engine drive for surface operation and electric dynamo for submerged running. Both small coastal defense submarines and larger faster fleet submarines used this basic design.
A first attempt at a fleet submarine in the US Navy was the T Class of 1916. These boats had four diesel engines to provide the required horsepower to drive the 268 foot long hull at the designed 20 knots. Two each were connected in tandem on each shaft. This proved too complex to be reliable. Another attempt at the large submarine design was the first three boats of what was loosely termed the V Class. Designed in 1920, these boats split the diesel plant so that two engines drove electric generators and were situated forward of the control room. Two other engines were situated aft in the standard direct drive configuration, one to each shaft. These 2000 ton boats had grown to over 330 feet in length. They proved to be unhandy in diving and maneuvering. Even in later life converted to be cargo carriers, the three were generally considered unsuccessful.
Throughout the 1920’s the submarine design community which consisted of constructors, submarine commanders and engineers worked to develop, build and test new designs in an atmosphere of disarmament. This work resulted in several designs which when built were to become the remainder of the V-Class. Argonaut or V-4 was built as a minelayer capable of carrying sixty Mk XI mines and laying these through two 40” diameter tubes in her stern. Two large cruiser submarines, the Nautilus and Narwhal were designated V-6 and V-7. These were very much similar to Argonaut but without the mine laying tubes. All three of these (V-5, 6, 7) carried the largest deck guns of any US submarine, the 6”/53 Mk XII Mod 2. These boats were plagued by early engine reliability problems and underwent engine replacements early in the war. The Dolphin or V-7 was to be less expensive than the six large boats that preceded her. She had a rearranged tankage and hull framing. Her internal layout was the forerunner of the standard model of fleet submarine. The last two of the V Class, Cachalot and Cuttlefish started the trend to welding. Electric Boat Company which built Cuttlefish used extensive welding throughout while Portsmouth Navy Yard retained riveting as the structural fastening method for Cachalot. These boats were smaller and lighter than any of the prior V Class and this proved to limit severely their speed, endurance and ease of repair and maintenance.
In the early 1930’s the Navy embarked on an ambitious plan of submarine design and construction. The result was a set of boats which used the lessons learned from building and operating the V Class and with an eye to the requirements of a submarine war which would take place over the vast ocean distances in the Pacific. The submarine commanders wanted more speed and endurance, better habitability to increase crew endurance, more torpedoes and torpedo tubes and larger deck guns. This had to be tempered with considerations of initial cost, manning and the constant tradeoffs of shaft horsepower, displacement and size. An unusual competition occurred between the private shipbuilder Electric Boat Company and the government's Portsmouth Navy Yard. Each were given the general design and specifications in the four boat FY 1934 build program and were to, separately, create the detailed design and prepare the contract designs. So the four boats were in essence prototypes of separate classes worked up from the same set of specifications. Each builder built two boats. Portsmouth built Porpoise and Pike. EB built Shark and Tarpon. This ‘unofficial’ competition proved to be beneficial in the rapid development of the fleet submarine through the 1930’s.
In essence, the evolution seen in design through the decade prior to WWII was seen through the differences in the Porpoise through the Tambor Class boats. This evolution culminated in the Gato and Balao Class designs which were the mainstay boats of the war years. Starting after the large Argonaut and Narwhal classes boats reverted to a generally common length around 300 feet and a beam of 24 to 27 feet. The major changes were in the number and location of torpedo tubes and the propulsion equipment arrangement and hull construction technique.
Torpedo tubes number and location started with four tubes forward and two aft with two additional tubes in deck tubes located in the forward superstructure. The evolution ended with six tubes forward and four aft. Propulsion equipment began with a combination of direct drive diesels and diesel generators in a single engine room space and ended with four diesel generators, two each of two engine rooms and the electrical controller cubical in a separate space with main propulsion motors in this compartment. Construction technique started with all riveted hull, superstructure and tankage and ended with all welded construction throughout. The changes are reflected in a general sense in the class designations but in reality they are overlapping and specific ships in a class may vary widely except in the major characteristics.
As had been said, the concept of requiring a 'fleet submarine' ended with the change in tactics of the boats during WWII. The wide ranging independent operations in support of but not traveling with the fleet, changed the way people visualized the role of the submarine.
The division of 'fast attack' and 'missile boat' made the 'fleet submarine' appelation even more remote. However, the 'fast attack' nuclear submarine is now what the early fathers had in mind. It can range ahead of and with the carrier battle group, clearing the road.