USS Cavalla

Cold War Missions

The Cavalla-Thresher Incident

Cavalla was at sea in the proximity of Puerto Rico, while the nuclear submarine USS Thresher was moored to the portside of Pier Fernandez Junos Bravo in downtown San Juan, Puerto Rico. At 10:20, Thresher was rigged for reduced electrical power, and 15 minutes later her reactor was shut down to "subcritical". This was done to give as many of the crew as possible liberty. Normally, electrical power for the ship's needs is supplied by cable from the pier while she remains moored in port. However, since San Juan did not have this facility, Thresher started carrying the electrical load on her diesel engine which operated a generator. The diesel was referred to as the Dinky because of its small size and reduced capacity compared to the reactor. At 2250 that night, 10hours 15 minutes after starting up, Thresher's diesel engine quit. The problem was a broken shaft in the fuel pump.

The OOD ordered power be taken from the batteries while the diesel was being repaired. While the spare parts were being searched for the batteries discharged too low to restart the reactor. But this process (starting the reactor) would take several hours, and meantime Thresher's interior temperature began to soar. In the absence of any air-conditioning, the temperature rapidly soared to 136 degrees F.

"Somehow the word got out to the men on liberty that all liberty was canceled and to report back to the ship as fast as possible," remembers LICS(SS) Keith A. Johnson, of the Thresher. "The crew was scattered who knows where around San Juan. Most of the men made it back in time to render assistance to the Thresher. I was in a casino and got the word and took a taxi back to the ship. As I approached, it was the first time I had any idea that an emergency was taking place. Ten or fifteen crew members were lying on the pier suffering from various stages of heat exhaustion and the corpsman were administering first aid. Someone, I don't remember who, ordered me to go below and relieve the man in the tunnel who had been there for some time. I was told I would be relieved in 15 minutes because of the 136-degree heat. My first recollections are trying to breathe in 136 degree heat was very difficult. As I approached the tunnel, I was soaked with perspiration and the person who I was to relieve was standing in his undershorts in a puddle of his own perspiration. It was dark and he handed me a battle lantern and told me to keep an eye on a water level indicator and report any changes on the sound-powered telephone to the maneuvering room. I immediately stripped down and proceeded to do as I was told. At this point I was standing directly above the reactor which I was told was reaching a critical temperature and could at any minute initiate emergency cooling and a possible melt down."

The Cavalla came to the rescue. Electrical cables were borrowed from the USS Cadmus (AR-4), a Vulcan class repair ship which happened to be in the harbor. Cavalla was moored close enough to Thresher to be able to use those cables as "jumpers" and use her diesels to give the Thresher the electricity to bring the reactor back to critical at 0402. Cavalla stayed alongside another two days and Thresher got underway on Monday, November 6, 1961.

Cavalla would go on to finish her career as a training boat while Thresher was not so fortunate. On April 10, 1963, Thresher was lost during advanced trials in two miles of ocean--America's first nuclear sub casualty.

Continue Cavalla in the 1960s