The submarines had a length of 175 feet (53.3m)overall, a beam of 16ft 7in (5.1m), and a mean draft of 13ft 11in (4.2m). They displaced497 long tons (505t) on the surface and 652 long tons (662t) submerged. The R-21-class submarines had a crew of 3 officers and 23 enlisted men. They had a diving depth of 200ft (61.0m).[2][4]
For surface running, the boats were powered by two 500-brake-horsepower (373kW)Busch-Sulzerdiesel engines, each driving one propeller shaft. When submerged each propeller was driven by a 400-horsepower (298kW)Diehl Manufacture Companyelectric motor. They could reach 14 knots (26km/h; 16mph) on the surface and 11kn (20km/h; 13mph) underwater. On the surface, the R-21-class had a range of 3,523 nautical miles (6,525km; 4,054mi) at 11kn (20km/h; 13mph), or 6,499nmi (12,036km; 7,479mi) if fuel was loaded into their main ballast tanks.[4]
Attached to Submarine Division1, R-21 operated out of the submarine base, at Groton, Connecticut. She conducted diving and approach tactical training in Long Island Sound, and conducted several training cruises in the vicinity of Block Island, with other units of the division. Following a recruiting cruise, to New Haven, Connecticut, and Bridgeport, from 20 August to 27 August 1919, she returned to New London, for upkeep.[5]
Following several practice dives out of Coco Solo, she transited the Panama Canal, on 27 January 1920, for drydock work at Balboa. Returning to Coco Solo, R-21 continued to refine her diving, approach, and torpedo tactics through the spring and summer. During two trips to Almirante Bay, 30 March-2 April and 17–20 May, she practiced with other units of the first division.[5]
R-21 again transited the canal, to Balboa, 27 September 1920, for a month in drydock. Upon returning to Coco Solo, she was laid up for 11 months of extensive overhaul. She sailed north, on 26 September 1921, via Guantanamo Bay, Key West, and New York City, arriving New London, on 27 October. She sailed to Portsmouth, New Hampshire, on 27 December 1920, for refitting.[5]
A successful test dive on 26 May 1922, meant that R-21 could return to New London. Through the spring and summer months she operated out of New London and Newport.[5]
The boats of Submarine Division1, sailed from New London, on 2 October 1922, for Coco Solo. R-21 served as flagboat as the vessels cruised via Hampton Roads, and Guantanamo. After 11 days out, R-24 developed engine trouble and was temporarily taken under tow by R-21. The Cuba-bound steamerSSBethore rendered assistance, and R-21 arrived at Coco Solo, on 27 October 1922.[5]
R-21 spent the rest of her active Navy days operating out of Coco Solo, and undergoing repairs at Balboa. She sailed from Coco Solo, for the last time, 15 February 1923, with the minesweeperQuail(AM-15), acting as tender, and eight other submarines. Two days later R-21's engines malfunctioned and she was towed into Guantanamo, by the tender. Repairs were quickly accomplished and R-21 sailed for the Philadelphia Navy Yard, on 22 February, arriving there via Charleston, South Carolina, on 9 November 1923.[5]
Fate
Decommissioned at the Philadelphia Navy Yard, on 21 June 1924, R-21 was struck from the Naval Vessel Register on 9 May 1930, and sold for scrap, on 30 July 1930.[5]
Priolo, Gary. "R-21 (SS-98)". Navsource.net. Retrieved 20 November 2025.
Gardiner, Robert & Gray, Randal (1985). Conway's All the World's Fighting Ships 1906–1921. Annapolis, Maryland: Naval Institute Press. ISBN0-85177-245-5.
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