The United States D-class submarines were a trio of submarines built for the United States Navy in the first decade of the 20th century. All three ships served during World War I providing training for crews and officers on the US East Coast, before the class was decommissioned and sold for scrap in 1922.
The D-class submarines were enlarged and iterative improvements over the preceding C class. They were built by the Fore River Shipbuilding Company, of Quincy, Massachusetts, under a subcontract from the Electric Boat Company, of Groton, Connecticut.
The D-class had a length of overall, a beam of and a mean draft of . They displaced on the surface and submerged. They had a diving depth of . The D-class boats had a crew of 1 officer and 14 enlisted men.
For surface running, they were powered by two Electric Boat/Craig gasoline engines, each driving one propeller shaft. When submerged each shaft was driven by a electric motor. Two 60-cell batteries provided power when submerged. They could reach on the surface and underwater. On the surface, the boats had a range of at and at submerged.
The boats were armed with four 18 inch (450 mm) torpedo tubes in the bow. They did not carry reloads for them. They were the first US submarines to have four forward torpedo tubes, which became the norm until the , which joined the fleet in 1940.
These vessels included some features intended to increase underwater speed that were standard on United States Navy (USN) submarines of this era, including a small sail and a rotating cap over the torpedo tube muzzles. For extended surface runs, the small sail was augmented with a temporary piping-and-canvas structure. This structure would be disassembled and taken below before diving. USN tactical doctrine of the time did not emphasize quick dives so this was not seen as a liability.
These were the first USN submarines internally subdivided into compartments. Narwhal and Grayling had four compartments (torpedo room, forward battery/berthing & control room, after battery/messing, and engine/motor room). Salmon was fitted with only two bulkheads leaving one large compartment in the middle that consisted of both battery wells and the control room. On Narwhal and Grayling the helm wheel was actually in the after battery compartment, as the placement of the aft control room bulkhead dictated this arrangement.
By 1918, the US involvement in World War I, and the perceived need to have submarines to support the war effort, prompted the USN to refit the rapidly obsolescing D-class submarines with diesel engines. New London Ship and Engine Company (NELSECO), Electric Boat's engine subsidiary, was fully committed in other submarine work and did not have the capacity. The Lyons-Atlas Engine Company was chosen as a sub-contractor and they built six copies of the NELSECO 120-V4FS engines at their Indianapolis, Indiana, plant. The re-engining took place at the Philadelphia Naval Shipyard, but was not completed in full until 1919. The D-class boats became the earliest USN submarines to be equipped with diesel engines, although the E-class were the first to be built with them.
Many distinguished naval officers commanded a D-class submarine early in their careers including Chester William Nimitz, Irving Reynolds Chambers, Owen Hill, Robert Henry English, and Donald Cameron Bingham.
The following ships of the class were constructed.