Reclassified AS-7 on 17 July 1920, "Rainbow" departed the Boston Navy Yard on 28 October 1920, made a brief call at the Portsmouth Navy Yard, Kittery, Maine, then reached Newport, Rhode Island, 6 November 1921 to commence tending the S-boats of Submarine Division 12. The submarine division shifted base to New York on 19 November and sailed the 30th bound by way of Key West, Guantanamo Bay, the Panama Canal and ports of Mexico, to San Diego, arriving on 9 February 1921.