When They Put a P-39 Nose on a Tiny Boat — Japanese Called Them “Devil Boats”
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The Ingenious Solution of Lieutenant Robert Lynch
In the dark waters off Cape Esperants on October 19, 1942, Lieutenant Robert Lynch, a 26-year-old officer of the U.S. Navy, crouched behind the wheel of PT48, his heart pounding with anticipation. This was not just another night patrol; the stakes were high. He spotted three Japanese Dhatsu barges slicing through the Blackwater, transporting 60 troops and ammunition to reinforce their stronghold at Guadalcanal. Each barge was equipped with a type 92 heavy machine gun and had armor thick enough to withstand rifle fire. Lynch knew that his four Mark 8 torpedoes, though formidable, would pass harmlessly beneath these shallow-draft vessels.
The grim reality of the situation weighed heavily on Lynch. The motor torpedo boat squadron had already lost six boats in the waters around Guadalcanal, and 17 sailors had paid the ultimate price. The pattern was all too familiar: PT boats would detect Japanese barge convoys, launch torpedoes, and watch as they missed their targets, only to be met with a hail of gunfire in return. The twin 50 caliber Browning machine guns mounted on PT48 were devastating against wooden fishing boats but proved ineffective against the steel-plated barges.
As American aircraft became increasingly vulnerable to Japanese defenses, the enemy adapted by using smaller, harder-to-detect barges. Desperate for solutions, some PT crews had even resorted to mounting single-shot Army M3 37mm anti-tank guns on their boats, but these makeshift solutions were far from effective. The real problem, Lynch realized, was mathematics—each barge could carry 60 fully armed troops or eight tons of supplies, and the Japanese were running 20 to 30 barges past Guadalcanal every night.
On October 20, Lynch took a bold step. He walked the wreckage-strewn Henderson Field at dawn, counting 23 wrecked P39 Aeracco Cobras, each with intact M4 cannons. He envisioned a radical solution: if he could mount one of these aircraft cannons on PT48, it could change the game. With no official channels to pursue, Lynch approached Commander Alan Calvert, commanding officer of Squadron 3, with his audacious idea. To his surprise, Calvert approved it, and by that afternoon, Lynch and his crew were scavenging cannons from the wrecked aircraft.
The task was fraught with challenges. Technical Sergeant James Kugan, who had experience maintaining P39 aircraft, led the effort to remove the cannons. Time was short; they had until nightfall to complete the installation. The work was grueling, and the tropical heat made it even more difficult. But with determination, they managed to salvage three M4 cannons by sunset.
Back on PT48, the crew faced the daunting task of mounting the cannon securely to withstand the recoil of firing. Chief machinist mate Donald Frey quickly designed a makeshift pedestal mount from scrap metal. It was crude, but it would hold the cannon. By 2:00 AM on October 21, PT48 was equipped with the first-ever aircraft automatic cannon mounted on a U.S. Navy patrol torpedo boat.
As the night wore on, Lynch and his crew prepared for their first combat test. At 11:55 PM, radar detected four surface contacts—Japanese barges. Lynch altered course, closing the distance. At 800 yards, Mitchell, the gunner’s mate, opened fire with the M4 cannon. The initial rounds struck the lead barge, puncturing its armor and igniting a fire that sent men leaping into the water. The sight was shocking and exhilarating; the cannon worked beyond anyone’s expectations.
The second barge attempted to retreat, but Lynch pressed on, closing to 600 yards. Mitchell fired again, and the results were catastrophic for the Japanese vessel. The explosion was massive, visible for miles, signaling the effectiveness of their improvised weapon. In just one engagement, they had destroyed two barges and disabled another, all without sustaining any casualties.
The news of PT48’s success spread quickly through Squadron 3. The salvaged cannons proved to be a game-changer, allowing PT boats to engage Japanese supply lines effectively. By late October, three more PT boats had similar cannons installed, and the innovation was rapidly adopted across the fleet. The psychological impact on Japanese barge crews was profound; they began to fear the “demon boats” with their heavy cannon fire.
As the weeks passed, the effectiveness of the 37mm cannon became clear. PT boats were now able to destroy Japanese barges at unprecedented rates, significantly disrupting supply lines. The Bureau of Ordnance took notice and began the process of formalizing the installation of these cannons on PT boats. By December 1942, the salvaged cannons had become standard equipment.
However, the journey was not without its challenges. The maintenance of the cannons was demanding, and crews had to learn to strip and repair them with minimal resources. Technical Sergeant Kugan played a crucial role in training PT boat gunners on maintenance procedures, ensuring that they could keep their weapons operational in the field.
By early 1943, the 37mm cannon had transformed the tactical landscape for PT boats in the Pacific. The combination of speed, mobility, and firepower allowed them to engage Japanese forces effectively. The statistics were staggering: PT boats equipped with the cannons achieved a kill rate six times higher than those without. American casualties were reduced dramatically as well.
The ingenuity displayed by Lynch and his crew not only saved lives but also changed the course of naval warfare. The 37mm cannon became a symbol of American determination and innovation in the face of adversity. It was a testament to the power of creative problem-solving in combat, demonstrating that sometimes, the most effective solutions come from the willingness to adapt and improvise.
Lieutenant Robert Lynch survived the war, earning the Navy Cross for his actions. He returned to civilian life, but the legacy of his innovation lived on. The story of the 37mm cannon on PT boats serves as a powerful reminder of the human spirit’s resilience in the face of overwhelming odds. It highlights the importance of adaptability and the impact of one individual’s vision on the larger tapestry of history.
