(Submarine No. 89: dp. 569 (surf.), 680 (subm.); 1. 186'2"; b. 18'; dr. 14'6"; s. 13.5 k. (surf.), 10.5 k. (subm.); cpl. 33; a. 1 3", 4 21" tt.; cl. R-1)

R-12 (Submarine No. 89) was laid down by the Fore River Shipbuilding Co., Quincy, Mass., 28 March 1918; launched 15 August 1919; sponsored by Miss Helen Mack; and commissioned at Boston 23 September 1919, Lt. F. J. Cunneen in command.

R-12 remained at Boston until she headed down the coast on 11 March to New London, whence she operated until the end of May. She then continued south to Panama; transited the Canal at the end of June; arrived at San Pedro in July; and with the designation SS-88, departed the California coast for Pearl Harbor at the end of August. Arriving 6 September 1920, she remained in Hawaiian waters, with occasional exercises on the west coast and off Johnston Island until 12 December 1930. On that date R-12 got underway for the east coast and returned to New London on 9 February 1931. She conducted exercises with Destroyer Squadrons of the Scouting Force into the spring, then following overhaul trained personnel assigned to the Submarine School. On 27 September 1932, she departed New London for Philadelphia where, after decommissioning on 7 December 1932, she joined other R-boats berthed there in the Reserve Fleet.

Some 7 1/2 years later (1 July 1940), R-12 recommissioned in ordinary and shifted to New London to complete activation. Recommissioned in full 16 October 1940, she sailed for Panama 10 December, arrived on the 23d, and into October 1941, patrolled the approaches to the Canal. On 31 October, she returned to New London and for the next 3 months operated off the New England coast. In February 1942, she commenced patrols to the south and for the next year operated primarily from Guantanamo Bay and Key West. During March and April 1943 she was back at New London, then in May she returned to Key West where she trained submariners for the remainder of her career.

Shortly after noon on 12 June 1943, R-12, while underway to conduct a torpedo practice approach, sounded her last diving alarm. As she completed preparations to dive, the forward battery compartment began to flood. The collision alarm was sounded. Orders were given to blow main ballast and close the hatches. But the sea was faster. In about 15 seconds R-12 sank, taking her 42 officers and men, including Brazilian observers to a watery grave. R-12 was officially struck from the Navy list 6 July 1943.