USS R-23 (SS-100), also known as "Submarine No. 100", was an R-21-class coastal and harbor defense submarines of the United States Navy commissioned after the end of World War I.
The R-boats built by the Lake Torpedo Boat Company, through , are sometimes considered a separate class, R-21-class, from those built by the Fore River Shipbuilding Company, through , and the Union Iron Works, through , R-1-class.
The submarines had a length of overall, a beam of , and a mean draft of . They displaced on the surface and submerged. The R-21-class submarines had a crew of 3 officers and 23 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 Diehl Manufacture Company electric motor. They could reach on the surface and underwater. On the surface, the R-21-class had a range of at , or if fuel was loaded into their main ballast tanks.
The boats were armed with four torpedo tubes in the bow. They carried four reloads, for a total of eight torpedoes. The R-21-class submarines were also armed with a single /50 caliber deck gun.
R-23s keel was laid down on 25 April 1917, by the Lake Torpedo Boat Company, in Bridgeport, Connecticut. She was launched on 5 November 1918, sponsored by Miss Ruth Jane Harris, and commissioned on 23 October 1919.
A little over a month after commissioning, R-23 departed New London, Connecticut, for her homeport of Coco Solo, in the Panama Canal Zone.
When the US Navy adopted its hull classification system on 17 July 1920, she received the hull number SS-100.
She was based in the Canal Zone, interrupting her service there only for overhaul periods at Balboa, and on the East Coast.
She returned to the United States for inactivation in the fall of 1924, arriving at the Philadelphia Navy Yard, on 1 December. R-23 was decommissioned on 24 April 1925, after only five-and-a-half years of service. She was berthed at League Island, until struck from the Naval Vessel Register on 9 May 1930, and sold for scrap in July, of the same year.