The R-12 had spent a good number of years in service to the USN. However, she spent over eight years in the reserve fleet in Philadelphia in order to keep the USN within the limits of submarine tonnage prescribed by the London Naval Treaty. As the war situation worsened in 1940 the decision was made to reactivate the R-12 and most of her sister boats and return them to the active fleet. After recommissioning R-12 operated out of a variety of ports, including New London, Bermuda, Panama, Guantanamo Bay, Key West, and Casco Bay, Maine.
On June 12, 1943 R-12 was underway in the Florida Straits from her base in Key West. She was conducting a training mission with numerous Navy students and two Brazilian Navy observers onboard. At 1223 that afternoon she was running on the surface to a torpedo firing area when word was received on the bridge that the forward battery compartment was flooding. The collision alarm was sounded to alert the crew to the flooding. The disaster unfolded extremely fast. The boat nosed downward and was gone in just a few seconds. Only five men on the bridge made it off the boat before she went under. A subsequent Board of Inquiry was unable to ascertain the exact cause of her sinking, but it is likely that a failure of her riveted hull somewhere in the forward battery compartment was the cause of her loss.
In the fall of 2010 the wreck of the R-12 was discovered by a team lead by explorer Tim Taylor and his wife Christine Dennison. Using a Remotely Operated Vehicle, they returned in 2012, 2013, and 2014 and thoroughly documented the wreck site. While they were unable to find the exact cause of the sinking, their findings reinforced the idea of a hull failure.
R-12 and two of her sisters at their berths at Submarine Base Pearl Harbor, approximately 1921-1922. All have special identification markings. R-16 has the circle and R-17 has the triangle.
National Archives photo.
R-12 backing out of her mooring at Pearl Harbor, early 1920's. In modern times, all of the undeveloped land in the background has been incorporated into the massive Naval Station Pearl Harbor and has been fully developed. That was not the case in those early years. The submarine base was actually isolated away from the rest of the shipyard.
National Archives photo.
R-12 underway off the rugged coast of one of the Hawaiian Islands, early 1920's. She doesn't appear to be anchored, but she isn't moving either.
National Archives photo.
R-12 making a static dive in the shallow waters of Magazine Loch, Pearl Harbor, Hawaii, early 1920's. This was a function performed to check recently overhauled hull fittings to ensure they are watertight, without risking the boat in deep water. When this photo was taken the R-12 was most likely sitting on the bottom. The water depth in Magazine Loch at that time was quite shallow.
National Archives photo.
R-12 at her berth at the finger piers at Submarine Base Pearl Harbor, early 1920's. The three horns visible on her forward deck above the folded bow planes are the transducers for the Y-tube passive sonar.
National Archives photo.
R-12 underway in April, 1942 somewhere in the Caribbean, possibly off Guantanamo Bay, Cuba. This would be how the boat looked when she was lost one year later.
National Archives photo 80-G-7252 via Sean Hert and Navsource.org
