Coco Solo
"R-21" spent the rest of her active Navy days operating out of Coco Solo and undergoing repairs at Balboa. She sailed from Coco Solo for the last time 15 February 1923 in company with a tender, , and eight other submarines. Two days later "R-21"s engines malfunctioned and she was towed into Guantanamo by the tender. Repairs were quickly accomplished and "R-21" sailed for Philadelphia, Pennsylvania, on 22 February, arriving there via Charleston, South Carolina, on 9 November 1923.