On the morning of March 3, 1943, a Japanese convoy was steaming south along the coast of New Guinea, bound for the fortress at Lae. Packed aboard the transports were more than six thousand troops, along with weapons, ammunition, and supplies meant to shore up Japan’s position on the island. Destroyers screened the formation, Zero fighters circled overhead, and the ships bristled with anti-aircraft guns. But sweeping in low over the wave tops came something the Japanese never expected: American B-25 Mitchell bombers that were no longer bombers in any conventional sense.

The glass noses had been ripped out and replaced with batteries of heavy . 50-caliber machine guns. More guns bristled from the sides of the fuselage. Instead of dropping bombs from thousands of feet, these aircraft came in at masthead height, pouring streams of fire across enemy decks, then releasing their bombs at point-blank range so the weapons skipped across the water and slammed into the hulls.

The tactic helped annihilate an entire convoy and turned the B-25 into one of the most feared low-level strike aircraft of the Pacific War. Behind that transformation stood a former naval aviator in his early forties whose wife and four children were prisoners of the Japanese. His name was Paul Irving Gunn. Everyone called him Pappy.

When the B-25 Mitchell entered service, no one had designed it for this kind of fighting. It was a conventional twin-engine medium bomber, which first gained fame in April 1942 when sixteen of them took off from the carrier Hornet to bomb Japan in the Doolittle Raid. But the campaign in the Pacific presented a very different kind of war, one fought across thousands of miles of ocean, jungle, and scattered islands. Strategic high-altitude bombing had little relevance there.

For the Japanese, ships were the lifelines of their empire, carrying troops, fuel, and supplies to their far-flung bases. If those ships kept reaching their destinations around New Guinea and the surrounding islands, American and Australian soldiers would keep facing a well-supplied enemy. The Allies had to sink them. For torpedo and dive bombers, the problem was straightforward.

For horizontal bombers, it was not. Hitting a maneuvering ship from high altitude depended largely on luck. The Fifth Air Force needed a better way, and its new commander, Major General George Kenney, believed he had the answer. Kenney took charge of Allied air forces in the Southwest Pacific in July 1942, inheriting an air arm stretched to the end of a very long supply line and plagued by grounded aircraft, missing spare parts, and punishing conditions.

Mechanics had to improvise constantly to keep planes flying. Among them was one of the most unconventional officers in the US Army Air Forces. At forty-three, Paul Gunn did not fit the image of a dashing young war hero. After a long military career, he had helped establish Philippine Air Lines, where he remained in early December 1941, running a civilian airfreight operation in South Asia with his wife and four children in Manila.

Then the Japanese attacked. Within weeks, their forces were advancing on the capital. Gunn was called into service with the US Army Air Corps, but the situation deteriorated so rapidly that he barely escaped to Australia. He could not get his family out.

His wife and children were interned at Santo Tomas in Manila. For Gunn, the Pacific War was no longer just a military campaign. It was personal. He had no way of knowing whether he would ever see his family again.

Kenney later described Gunn as waging what amounted to a private war. What Gunn understood, above all, was aircraft. The technique of skipping bombs across the water had one major problem: it required the attacking plane to fly very low and straight toward its target, which made the bomber an easier target the closer it came. The aircraft had to blast its own way to the release point.

Gunn first experimented with the Douglas A-20 Havoc, removing the standard nose arrangement and mounting a forward-firing battery of . 50-caliber guns salvaged from wrecked fighters. Kenney saw the potential and put him in charge of special projects. The goal was not simply to shoot at ships but to solve the most dangerous part of the entire low-level attack: the approach.

If a plane could overwhelm a ship’s deck with heavy fire while closing in, the Japanese gunners would have to choose between taking cover or dying. The guns would not replace bombs; they would clear the way for them. It was a simple concept. Turning a plane capable of doing it was something else entirely.

The B-25 had never been designed to carry a concentrated battery of heavy machine guns firing straight ahead. The bombardier’s compartment had to be removed to make room for eight fixed forward-firing guns, and the top turret could also be locked to fire forward, meaning a single Mitchell could aim up to ten . 50-calibers at an enemy ship. The added weight, vibration, recoil, and balance created new problems, but after repeated testing and adjustments, the planes flew and the guns worked.

Kenney called the modified bombers commerce destroyers. Gunn and his men called them warships. They needed a target to prove their destructive power. In early March 1943, the Japanese tried to reinforce Lae.

More than six thousand troops and their supplies were loaded into a convoy of eight transports screened by destroyers. If they arrived, Japan’s position in New Guinea would be considerably strengthened. Navy codebreakers intercepted messages revealing the convoy’s destination and arrival date. Kenney ordered round-the-clock reconnaissance and moved as many aircraft as possible to forward airfields.

Around three in the afternoon on March 1, a B-24 Liberator on patrol spotted the convoy off the north coast of New Britain. The Battle of the Bismarck Sea was about to begin. The next day, twenty-eight heavy bombers attacked from five thousand feet and sank one transport. At sunrise on March 3, the convoy was heading south along the New Guinea coast, now within range of the medium bombers.

Around ten in the morning, twelve of Gunn’s new B-25s took off with other aircraft and flew toward the Japanese ships. This attack would be different. High-level bombers struck first, hitting nothing but forcing the ships to scatter, which exposed them to Australian Beaufighters sweeping in at masthead height and raking the vessels with their machine guns. Directly behind them came the B-25s, low and fast and heavily armed.

As each Mitchell approached over the waves, ten . 50-calibers fired almost simultaneously. The whole aircraft shuddered as a stream of fire swept across the hull and decks. Crews fell dead beside their guns.

Deck cargo caught fire. Superstructures collapsed and burned. Then, at the last moment, bombs were dropped to skip across the surface and crash into the side of the ship. The bomber pulled up and climbed over the mast while another B-25 closed in.

The Japanese convoy was overwhelmed. More than a hundred aircraft attacked from different heights and directions, and follow-up strikes that afternoon, supported by A-20 Havocs and Bostons, finished off whatever transports were still afloat. By nightfall, every transport had been sunk, and four of the escorting destroyers never returned to base. Over the following three days, survivors were systematically hunted down among the wreckage and the sea, roughly a thousand men in lifeboats or clinging to debris.

The attempt to reinforce Lae had become a catastrophe, ending any realistic Japanese hope of holding New Guinea. The battle proved that heavily armed medium bombers, flown aggressively at extremely low altitude, could destroy ships. The success was so emphatic that manufacturers took notice. North American Aviation incorporated elements of the field modifications into the Mitchells coming off the production lines, and experimental variants even mounted a 75-millimeter tank cannon in the nose, though the heavily gunned versions proved far more effective.

By August 1943, units like the 345th Bomb Group were converting from conventional medium bombing to the low-level strafing and skip-bombing role that became their signature. Across the Southwest Pacific, the sight of B-25s approaching at wave-top height became increasingly familiar. The Mitchell had become something its original designers never imagined: a devastating anti-shipping gunship. Throughout all of it, Gunn’s private war continued.

His wife and children remained in Japanese hands, held behind the barbed wire of Santo Tomas for more than three years. They were not liberated until February 1945, when American troops finally entered Manila. For Gunn, every advance across the Pacific had been a step toward them. Every Japanese position pushed back, every island taken, every ship sunk, moved the war closer to the city where his family was imprisoned.

The same man who had watched his family disappear behind Japanese lines in 1942 spent the intervening years helping devise some of the weapons used to fight his way back to them. After the war ended, Gunn returned to the Philippines and rebuilt his career with Philippine Air Lines. On October 11, 1957, his plane crashed in a storm over the Philippines. There were no survivors.

But the legacy of his work lived on in the low-level gunships that helped break Japan’s grip on the Pacific, and in the crews who flew them through curtains of fire to deliver their bombs at masthead height.