|Ordered:||29 August 1916|
|Laid down:||16 June 1917|
|Launched:||8 January 1918|
|Commissioned:||11 September 1918|
|Decommissioned:||19 September 1945|
|Fate:||sold for scrap|
|Displacement:||569 tons surfaced, 680 tons submerged|
|Length:||186 feet 2 inches|
|Draft:||14 feet 6 inches|
|Speed:||13.5 knots surfaced, 10.5 knots submerged|
|Complement:||29 officers and men|
|Armament:||one three-inch gun, four 21-inch torpedo tubes|
Following shakedown, R-18 was assigned, briefly, to the Panama Canal Zone. At the end of the year, 1918, she returned to California. At San Pedro, California, from January to March 1919, she then underwent overhaul at San Francisco, California, and on 17 June got underway for Hawaii. On 25 June she arrived at Pearl Harbor. Based there for over a decade, she served with the fleet, training personnel and testing new submarine equipment. In July 1920 she was given hull classification symbol SS-95.
R-18 departed Hawaii 12 December 1930, transited the Panama Canal, thence continued on the East Coast for inactivation. Arriving at Philadelphia, Pennsylvania, on 9 February 1931, she was decommissioned 13 May and berthed at League Island until after the outbreak of World War II.
Recommissioned 8 January 1941, R-18 was at New London, Connecticut, for reconditioning and fitting out into May. On 12 May she got underway for the Canal Zone where she patrolled into September. In October, she returned to New London, whence after overhaul, she conducted training exercises in submarine and antisubmarine warfare. In early January 1942, she shifted her training activities to the Casco Bay, Maine, area. Then, later in the month, she added patrols along a line between Nantucket Light and Bermuda to her schedule.
Then assigned, with others of her class, to training duties for the remainder of the war, R-18 returned to New London on 24 December. She operated in the New London and Portland, Maine, areas until June 1943. The last six months of the year were spent at Bermuda. From January through March 1944, she was back in southern New England; then, in April she moved south for eight months at Key West, Florida, and Port Everglades, Florida.
With the new year, 1945, the submarine again began operations out of New London. During the following summer she made her last voyage to Florida and back and in September she headed for New Hampshire and inactivation. R-18 arrived at Portsmouth, New Hampshire, on 7 September and was decommissioned on 19 September. Struck from the Naval Vessel Register the following month, she was sold for scrapping to the John J. Duane Company of Quincy, Massachusetts, in 1946.