A tragic accident occurred on September 26, 1921 when the submarine USS R-6 SS-83 sank to the bottom of the harbor at San Pedro, California. Two crewmen had made adjustments to a torpedo which was to be used in an upcoming practice, and when they attempted to put the fish in the tube the sea began to flood the boat. She began to settle quickly and the men began to abandon the boat. The boat was alongside USS Camden AS-6 with several other submarines and the hawsers between R-6 them were cut by an alert sailor thus keeping any other boat being dragged down with her.

Eighteen men got out of the boat, but sadly two men were lost. One was trapped in the boat the other was reportedly shot out of the hatch into the sea. He however could not swim and panicked even refusing help from others and drowned. The bodies of both men were later recovered.

It was determined after the boat was raised on Oct. 13 that the outer door was open and that the interlocking mechanism between the outer and inner torpedo doors failed allowing the boat to flood. R-6 was repaired and placed back in active service. Other than a decommission period she remained in service through the Second World War, mostly in a training roll. She was sold and scrapped in 1946.