On September 26, 1921 R-6 sank at her mooring in San Pedro Harbor, California, due to a "malfunction" in one of her torpedo tubes. USN submarine torpedo tubes have an interlock system that prevents both the breech and the muzzle end of the tube from being opened at the same time. Either this system did not operate like it should have (very unlikely), or the interlock system had been deliberately disengaged for some reason and both ends of the tube were mistakenly opened (likely). This would have flooded the boat very quickly. As far as we can determine no one was killed or injured in this accident. This photo shows R-6 alongside the R-10 with her bow sticking up above the water and with her stern sunk to the bottom. The minesweeper USS Cardinal (AM-6) is standing by in the background.
USN photo in the private collection of Ric Hedman
The combined efforts of the crews of the R-10 and the Cardinal sealed up the R-6 and pumped out the water. She was fully raised on October 13, 1921 and towed to the Mare Island Navy Yard for reconditioning. Surprisingly she had suffered little damage and after a thorough drying out and cleaning was put back into full service.
