(SS-21: dp. 330; l. 142'7"; b. 15'5"; dr. 12'2"; s. 14 k.; cpl. 22; a. 4 18" tt.; cl. F)
SS-21, originally named Barracuda, was renamed F-2 on 17 November 1911 and launched 19 March 1912 by Union Iron Works, San Francisco, Calif.; sponsored by Miss A. R. Rolph, daughter of the mayor of San Francisco; and commissioned 25 June 1912, Lieutenant (junior grade) F. L. Chew in command.
F-2 joined the 1st Submarine Group, Pacific Torpedo Flotilla, in operations between San Diego and San Pedro, the Flotilla's base. She continued to play an important part in developing tactics and coordinating the use of underseas craft with the fleet during an extended training period in the Hawaiian Islands, from August 1914 through November 1915.
After lying in ordinary at Mare Island between 15 March 1916 and 13 June 1917, F-2 became flagship of Division 1, Submarine Force, Pacific Fleet. Returning to operations out of San Pedro, she participated in surface and submerged exercises, torpedo proving practice, experiments in balancing at various depths, and trained prospective crews of new submarines. On 18 September 1919, she was placed in reserve commission at San Pedro to be used in elemental school work until decommissioned at Mare Island 15 March 1922. She was sold 17 August 1922.