19. Mine detecting sonar made it possible to enter previously closed waters around Japan
The sonar developed throughout 1944 detected small objects, including mines, and notified the operator with a clear blip on a screen, as well as a clearly audible ringing tone. Submariners immediately dubbed the sonar “Hell’s Bells”. The sonar worked on the basis of a frequency modulated (FM) radio signal, rather than an active sonar ping and return. By the end of December 1944, Lockwood’s confidence in the device led him to suggest to Admiral Ernest J. King, Chief of Naval Operations, that it could open the Sea of Japan to submarine incursion. King approved the plan Lockwood proposed, conditionally based on reliability improvements and the endorsement of CINCPAC.
In the spring of 1945, several US submarines equipped with the Hell’s Bells sets began probing the Tsushima Strait, one of the heavily mined entrances to the Sea of Japan. By April, American charts indicated four rows of underwater mines in the straits. In late May and early June, nine American submarines entered the Sea of Japan as part of Operation Barney, all equipped with Hell’s Bells sonar. One, USS Bonefish, sank during the operation, which saw the destruction of 28 Japanese ships, including a submarine and a destroyer. They also sank a Russian ship, leading to a diplomatic incident, since Russia was officially neutral as regarded the Pacific War at the time.