USS L-6 (SS-45), also known as "Submarine No. 45", was an L-class submarine of the United States Navy. She worked on exercises off the West Coast, prior to sailing to the Azores, during WWI. After the war she transferred back to the Pacific, where she worked with experimental torpedoes and underwater detection equipment.
The L-class boats designed by Lake Torpedo Boat (L-5 through L-8) were built to slightly different specifications from the other L boats, which were designed by Electric Boat, and are sometimes considered a separate L-5 class. The Lake boats had a length of overall, a beam of , and a mean draft of . They displaced on the surface and submerged. The L-class submarines had a crew of two officers and 28 enlisted men. They had a diving depth of .
For surface running, the boats were powered by two Busch-Sulzer diesel engines, each driving one propeller shaft. When submerged each propeller was driven by a electric motor. They could reach on the surface and underwater. On the surface, the Lake 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 carried four reloads, for a total of eight torpedoes. The L-class submarines were also armed with a single /23 caliber on a disappearing mount.
L-6s keel was laid down on 27 May 1914, by the Craig Shipbuilding Company, in Long Beach, California. She was launched on 31 August 1916, sponsored by Mrs. Katherine Monroe, and commissioned on 7 December 1917.
After exercises along the West Coast, L-6 departed Pacific waters on 20 April 1918. She reached Charleston, South Carolina, on 10 June. Following a brief overhaul, the submarine patrolled off Charleston, until she sailed on 15 October, for the eastern Atlantic. Arriving Ponta Delgada, Azores, in early November, L-6 joined Submarine Division 6, just prior to the signing of the Armistice with Germany on 11 November.
After making stops in Caribbean Sea, and Central American ports, L-6 arrived San Pedro, California, on 14 February 1919, completing one of the best long-distance seagoing performances of the United States's youthful submarine force. From 1919 to 1922, she remained on the West Coast, experimenting with new torpedoes and undersea detection equipment, during which time she was redesignated from "Submarine No. 45", to SS-45, on 17 July 1920.
L-6 was placed in commission, in ordinary, on 24 March 1922; returned to full commission on 1 July; and sailed for the East Coast the same month. Upon arrival Hampton Roads, L-6 decommissioned on 25 November 1922, and was sold to M. Samuel and Sons, on 21 December 1925, for scrapping.