R-2 was transferred to the United States Pacific Fleet on 14 April 1921, transited the Panama Canal on 28 May 1921, and arrived on 30 June 1921at her new base, San Pedro, California. She took part in fleet exercises off Central America from 5 February to 6 April 1923. Returning to San Pedro on 10 April 1923, R-2 was ordered to Hawaii on 16 July with submarine Division 9 and remained there for eight years, developing submarine tactics with the Pacific Fleet. She made an endurance cruise to Midway Atoll in the Northwestern Hawaiian Islands in July and August 1924.
Leaving Pearl Harbor, Hawaii, on 12 December 1930, R-2 was reassigned to the Atlantic Fleet and arrived at New London via the Panama Canal on 9 February 1931. She was attached to Submarine Division 4 and for the next ten years served as a training ship for the Submarine School at New London and for the Yale UniversityNaval Reserve Officer Training Corps unit.
Assigned to Submarine Division 12 on 1 June 1941, R-2 departed New London on 16 June and arrived on 22 June 1941 at Key West, Florida, her new home port. Based there for the remainder of her career, she was attached to the Fleet Sonar School, and assigned periodically to defensive patrols in keeping with her limited operational capabilities.