Completed and fitted out at Boston, Massachusetts, during the summer and early fall of 1919, R-7 got underway for New London, Connecticut, and duty with SubDiv 9 on 21 October.

Given hull classification symbol SS-84 in July 1920, she again headed south on 13 September this time for overhaul at the Norfolk Navy Yard until April 1921.

Ready for sea in early April, she moved south in May and conducted patrols in the Virgin Islands and off Panama into the fall.

On 8 October she returned to New London, underwent overhaul, and at the end of November began a series of anti-submarine patrols in the shipping lanes between Bermuda and the northeastern coast.

She maintained those patrols through the German anti-shipping offensive of 1942 alternately basing her operations at Bermuda and New London.