The Desperate Naval Struggle in the Pacific

By early 1945, the Pacific War had reached a critical phase. With Allied forces advancing toward Japan’s home islands, the Imperial Japanese Navy resorted to desperate measures—extensive minefields laid across strategic choke points like the Tsushima Strait. These underwater barriers threatened to cripple American submarine operations, which had been devastating Japanese supply lines. The U.S. Navy responded with an urgent program to train submarines in mine detection and evasion using cutting-edge FM sonar technology.

Training Under Fire: The Perilous Experiments

In March 1945, the submarine USS Tunny (SS-282) became a testbed for high-stakes mine-detection drills off Saipan. Commanded by Lieutenant Commander George Pierce, the crew grappled with temperamental sonar equipment that alternated between breakthroughs and maddening failures. Professor Malcolm Henderson from the Naval Laboratory in San Diego oversaw the trials, tweaking condensers and relays to stabilize the system.

A key innovation involved suspending dummy mines from buoys at 42 feet—simulating real threats in deep waters where anchoring was impossible. Early attempts were disastrous; the sonar frequently failed to register targets. Yet persistence paid off. After a night of adjustments, Tunny’s crew achieved reliable detections, proving the FM sonar could—under the right conditions—navigate minefields.

Allied Cooperation and Technological Exchange

The campaign drew unexpected allies. British Rear Admiral George Creasy, though inexperienced in submarine warfare, arrived in Guam with a skeleton staff (and misplaced luggage) to share Britain’s ASDIC sonar technology. This device had helped clear Italian mines off Sicily in 1943. While ASDIC had limitations—it emitted detectable pulses and produced ambiguous readings—its principles informed U.S. refinements.

Meanwhile, British XE-class midget submarines, transported aboard HMS Bonaventure, prepared for operations in Subic Bay. The Anglo-American collaboration underscored a shared urgency: Japan’s minefields threatened not just submarines but also the looming invasion of Okinawa.

Triumph and Tragedy: Breaking the Barrier

The turning point came when Tunny, armed with FM sonar, successfully charted 222 mines in the East China Sea—though post-mission analysis revealed some “mines” were actually sunken oil drums. The feat earned praise from Admiral Chester Nimitz, but losses mounted. The USS Trigger (SS-237), a veteran sub with two Presidential Unit Citations, vanished after a depth-charge attack off Kyushu on March 28.

Other submarines faced surreal dangers. The USS Devilfish (SS-292) survived a kamikaze strike—the first recorded against a U.S. sub—while the USS Bang (SS-385) narrowly escaped a Japanese minelayer in a close-range gunfight. These episodes highlighted the chaotic asymmetry of the war’s final phase.

The Legacy of the Mine-Detection Campaign

The FM sonar program’s success reshaped undersea warfare. By April 1945, equipped subs could actively avoid mines rather than blindly risk entanglement—a tactic borrowed from British WWI experiences in the Dardanelles. The technology also paved the way for postwar mine-countermeasure strategies.

Yet the human cost lingered. The mistaken sinking of the Awa Maru—a Red Cross-sanctioned vessel—by the USS Queenfish (SS-393) in April underscored the fog of war. Though the error stemmed from faulty communications and heavy fog, it risked brutal Japanese reprisals. Ultimately, Japan’s collapse spared prisoners from retaliation.

Conclusion: A Hidden Turning Point

The 1945 mine-detection campaign was a quiet but pivotal chapter in the Pacific War. It exemplified Allied innovation under pressure and the unheralded risks submariners faced beyond torpedo duels. As historian Clay Blair noted, “Breaking Japan’s mine barriers required equal parts science, courage, and luck”—a triad that defined the submarine force’s unsung contribution to victory.

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