The “Devil Boat”: How a Fighter-Nosed PT Boat Annihilated a Japanese Supply Convoy in Minutes

December 13th, 1942, South Pacific, 4:17 a.m. Before the first light of dawn, three Japanese Dihhatsu landing barges were creeping along the shadows of the island coastline. Their mission was simple. Get supplies to the shore. Their confidence was high. There was no airfield nearby, no heavy artillery, and not even a decent patrol boat in sight.

Then, without warning, the lead barge erupted. It wasn’t the towering splash of a shell or the low thud of a torpedo. It was a stream of tracer rounds, firing with an unnatural density from a point just inches above the water. They skipped across the surface like a red-hot flame zipper, tearing the barged to pieces.

The engine room ignited instantly before the soldiers on deck could even react. A second burst rad the cockpit. Within 3 seconds, the first barge was dead in the water. Through his binoculars, the Japanese officer saw something he would never truly understand. The source of the fire wasn’t a warship. It wasn’t a plane. It was a lowslung wooden mosquito boat sitting almost flat against the waves.

Soldier memoirs

It had no turrets, no armor. Yet from its bow, it spat a kind of aerial firepower that belonged only in the sky. It was the fury of a fighter aircraft. Minutes later, the second barge was hit. Then the third, the tracers became a metal storm, shredding the decks from point blank range and turning the ships into burning wreckage.

Survivors later wrote in their reports, “The enemy utilized an unidentified weapon with extreme concentration and rate of fire.” “It resembled an aircraft, but it moved consistently along the surface of the sea.” What they didn’t know was that it wasn’t just like an aircraft. It was literally a piece of one.

Mounted to the bow of that small boat wasn’t a naval weapon, but the entire nose cannon assembly from a P39 Araco Cobra, aerial machine guns, concentrated bore sighting, and a killing structure designed for high-speed dog fights transplanted directly onto the water. No air superiority, then strip the planes and use them on the waves.

No warships, then give a small boat the punch of a fighter jet. In a theater of war where resources were scarce and supplies were always a step behind, frontline personnel made a decision that sounded borderline insane, they bolted the nose of a P39 onto a boat. That night, the Japanese realized for the first time, even if you escaped the skies, you couldn’t hide from the fighters of the sea.

Since September 1942, the Japanese had been running nightly supply runs through the channel known as the slot. The Americans called it the Tokyo Express. Destroyers and fast cruisers transported troops, ammo, and food under the cover of darkness. When American bombing made destroyer runs too risky, the Japanese switched to barges, smaller, harder to detect, and with steel plating thick enough to stop rifle fire and immune to PTBOT torpedoes.

The PT48 was equipped with four Mark 8 torpedoes. Each weighed over 2,000 lb with a 466-lb TNT warhead. However, the Mark 8’s depth control was notoriously unreliable in shallow water. When set for a shallow run, they often dove deeper or failed to stabilize before passing under the target. Against Japanese barges with a draft of only 5 ft, these torpedoes were virtually useless.

By midocctober 1942, Lieutenant William Bill Harper’s motor torpedo boat squadron 3 had lost six boats in the waters of Guadal Canal. 17 sailors had been killed. The pattern of combat was frustratingly repetitive. The PT boats would find a barge convoy, attempt a torpedo run. The torpedoes would miss, the barges would return fire, and the PT boats would either retreat or be set ablaze.

The PT48’s twin50 caliber Brownings fired 850 rounds per minute. They were devastating against wooden fishing boats, but against armored diehhatsu barges, they were useless. The 050 cal slugs just sparked off the steel plating. Commanders at Tulagi were desperate for a solution. Some crews tried mounting singleshot Army M337 mm anti-tank guns to the bow.

They removed the wheels and lashed the barrel to wooden planks. It was a fire once, reload manually affair. The damage to the barges was negligible. Lieutenant John F. Kennedy, commanding PT 109, had installed one of these anti-tank guns before a patrol in August. It barely worked. Kennedy’s crew could get off one shot, but they had to reload manually while being rad by Japanese machine gun fire.

It was dangerous and inefficient. The core of the problem was math. A single Dhatu barge could carry 60 fully armed soldiers or 8 tons of supplies. 20 to 30 barges passed through Guadal Canal every night. PT boats had to sink multiple barges in a single patrol to break the supply line. A singleshot gun couldn’t do that.

Henderson Field sat 3 mi inland from Lunga Point. The Marines had captured it on August 7th. By October, it had become a plane graveyard. The runways were lined with the husks of scrapped aircraft. The Japanese sent Betty bombers and zero fighters to strike almost daily. American pilots scrambled everything that could fly.

P 39s and F4Fs to intercept. Damaged planes crashed on landing. Some burned, others were simply written off. Dozens of Bell P39 Araco Cobra Rex were scattered around Henderson. It was an eccentric design. The engine was mounted behind the pilot with the propeller drive shaft running under the cockpit floor.

This unusual configuration left a massive space in the nose for an Oldsmobile M437mm autoc cannon with the barrel firing through the center of the propeller hub. The M4 had a fire rate of 150 rounds per minute fed by a 30 round horseshoe magazine with a muzzle velocity of 2,000 ft per second. Designed to shred light armor and aircraft, its firepower was terrifying.

Most of the P39 Rex at Henderson were total losses. Engines seized, wings snapped, fuselages broken, but the cannons were often pristine. The hydraulic recoil systems, the feed mechanisms, the barrel assemblies, everything was there. At dawn on October 20th, Harper walked through the graveyard.

He counted 23 scrapped Aeraccobras. Mechanics had already stripped the useful gauges, radios, and cables. But nobody had touched the cannons. They were aerial weapons. There were no mounting brackets for a boat, no technical manuals for naval use, and certainly no official authorization. Harper stood by a P39 whose nose was buried in the coral sand.

The 37mm barrel poked out like a steel finger. He did the math in his head. 150 rounds per minute, 30 round magazine, full auto. He looked back toward the water where PT48 was mored. His three mechanics were watching him. They knew exactly what he was thinking. At 2 p.m. that afternoon, Harper found Squadron 3 Commander Alan Calbertt.

There were no forms to fill out, no procurement process, and no formal channels. Just a simple question and an urgent need. By 4:30 p.m., four PT boat crews were at Henderson Field with cutting torches and wrenches. They had to finish before nightfall. An Oldsmobile M4 cannon weighed 213 lb without ammo.

The hydraulic recoil system added 40 lb and the feed mechanism another 30. A complete assembly weighed about 280 lb. The PT48, an 80 ft Elco boat, had a wooden hole made of two layers of 1-in mahogany. The deck was 3/4in plywood over frames spaced 2 ft apart. Naval engineers had calculated the load for a 050 cal machine gun turret, but no one had calculated the impact of a 280lb autoc cannon firing at 150 rounds per minute.

Sergeant James Walker, an aviation ordinance man at Henderson, who had worked on P39s back at Selfridge Field in Michigan, knew every bolt and hydraulic line of the Araco Cobra. When Harper’s team arrived, Walker was their first find. The first P39 they approached had a 20mm shell hole through the cockpit from 3 weeks prior.

The pilot had died instantly. Walker crawled into the nose with wrenches and a torch. The M4 was secured to the engine reduction gear housing by eight high-strength steel bolts. Each required a 15/16in socket. Walker only had a 3/4 in one. But in wartime, you made it work. Removing the gun meant disconnecting hydraulic lines, charging cables, feed shoots, and the trigger wire before cutting through the engine mounts.

Dismantling one plane took 2 hours. They had 6 hours of daylight left. Harper assigned eight men to the task, working in pairs. If everything went well, they’d have four guns by dark, but reality is rarely smooth. The second P39 had been baking in the tropical heat for 11 days. The hydraulic fluid had seized.

The charging cables were rusted shut. When Walker’s team tried to unbolt the gun, the bolts were frozen by thermal expansion. They needed penetrating oil, but the airfield had none. They poured aviation gasoline over them and waited 20 minutes. The bolts finally gave way. By 5:30 p.m.

, they had three complete M4 units sitting on the coral ground next to the runway. Walker inspected the hardware. The first gun had a hairline crack in the hydraulic recoil cylinder. Useless. The second had a bent feed pole. Fixable with a file in 30 minutes. The third was perfect. There was no mount for an aerial cannon on a PT boat.

The deck in front of the chart house was flat plywood over oak stringers. Harper needed a base that could absorb the recoil, allow for 360° rotation, and survive the shock of a boat slamming through waves at 40 knots. The machine shop at Henderson had only one lathe, one drill press, and a welding rig powered by a diesel generator.

They had repaired engine mounts and propeller hubs, but now they had to build a weapon system from scratch. Master Sergeant Donald Thomas spent 40 minutes sketching a mount with a grease pencil on an aluminum sheet. The design had to be simple. A 12-in diameter steel base plate, four bolt holes aligned with the deck frames, a vertical pipe welded to the plate, a rotating collar with a bearing surface, and a cradle for the gun.

All parts were salvaged from the landing gear scrap of wrecked planes. Thomas’s team began welding at 6:15 p.m. Because of diesel rationing, the generator kept cutting out. They had to weld for 5 minutes and then wait. The base plate took 40 minutes. The vertical pipe took 30. The rotating collar took an hour because the bearing surface had to be ground flat or the gun would jam.

By 900 p.m., they had a crude mount. It looked like a high school shop project. The welds were ugly, the paint was scorched, and the collar had a 3° wobble, but it could hold 280 lb of gun. And it could turn. It would have to do. They loaded the cannons and mounts onto a 6×6 truck. Three sailors sat in the back, holding the guns steady to prevent them from being damaged on the pothole road to the wararf.

PT48 was waiting across Ironbottom Sound at Tagi. The truck reached the Lunga Point Wararf at 10:30 p.m. and a Higgins boat fied the gear across. Harper met them at the dock. His crew had already marked the installation spot. The frames under the deck were double layered oak, strong enough for a machine gun turret and maybe strong enough for this.

They would only know if the deck would crack once the first shot was fired. Installing the mount required drilling four holes through plywood and 2 in of oak. They only had a handc cranked drill. Each hole took 30 minutes. By 1:15 a.m. on October 21st, the mount was secured. They hoisted the cannon onto the cradle.

The collar fit and the bracket was steady. The barrel could elevate and traverse. Not smoothly, but it moved. The ammo was the next problem. The M4 used 30 round horseshoe magazines originally stored in a compartment behind the P39 cockpit. A loaded magazine weighed 40 lb. PT48 had no magazine racks. They simply stacked six loaded magazines on the deck next to the gun.

In combat, the loader would have to hand feed them while the gun was firing. It was primitive, but it worked. At 2:00 a.m. on October 21st, 1942, PT48 became the first boat in the US Navy equipped with an aerial autoc cannon. It had taken only 9 hours from scavenging the wreck to final installation. The gun had never been test fired.

The mount hadn’t been stress tested, and the crew had no training. None of that mattered. The Japanese barges were moving tonight. At 10 p.m. PT48 left to logi. Squadron 3 sent four boats PT40, PT46, PT48, and PT60. They split up. Two north of Tsavo Island, two at Cape Espiron. Harper was in command of PT-48 with its untested 37mm cannon.

Gunner’s mate, second class. Harold Horton volunteered to man the gun. Horton had spent 12 combat patrols using 050 cal machine guns. He had never touched an aerial autoc cannon. No one on the boat had. Walker’s only instructions at the dock were simple. Aim, pull the trigger, and swap magazines when it’s empty. The hydraulics would take the kick.

Hopefully, it was an overcast night with no moon. Visibility under the starlight was about 200 y. The sea was calm. PT48 cruised on muffled engines to hide its noise and wake. The 37mm pointed forward. Horton sat on an ammo crate, six magazines at his side. At 11:55 p.m., radar picked up surface targets at 320°, 4,000 yd out.

Four blips moving at 8 knots. The signature matched supply barges. According to the manual, a PT boat should close to 1,000 yd to fire torpedoes, 800 yd for the best hit probability, but that would also expose them to return fire against barges that torpedoes couldn’t hit anyway. The manual was irrelevant. Harper had to get Horton into range.

At 3,000 yd, the barges appeared as silhouettes against the dark water. Four A type Dhatsu barges were in single file. Each was 49 ft long, 14 ft wide, powered by a single diesel engine. Max speed 12 knots. Each was armed with a type 92 heavy machine gun. The barges were packed with soldiers. PT48 closed to 1,500 yd.

Soldier memoirs

Horton manually pulled the charging handle. The mechanism clicked. The first round was chambered. He flipped the safety. At 1,000 yd, the Japanese barges spotted PT48. Their type 92s opened up 7.7 mm rounds, splashing the water 30 yard ahead of the boat as orange tracers cut through the night. Harper didn’t veer off.

He was all in. At 800 yd, Horton opened fire. The 37mm cannon let out a roar. The muzzle flash illuminated the entire for deck. The recoil slammed into the gun body, making the deck shutter. The mount held. The shells flew in a rapid fire sequence. Horton held the trigger down. The M4 thundered at 2.5 rounds per second.

The 30 round magazine was empty in 12 seconds. High explosive shells tracked straight into the waterline of the lead barge. Every hit was an explosion. The first three rounds shredded the steel plating like paper. The fourth exploded inside the troop compartment. The barge’s fuel tank ignited instantly, a pillar of fire erupting from the center.

Japanese soldiers threw themselves into the sea. The barge coasted another 50 yd on fire before the bow dipped and it settled into the water. Horton yanked the empty magazine. The horseshoe system detached cleanly. He grabbed the second magazine and slammed it home. The reload took 8 seconds.

seconds that felt like an eternity in combat, but it worked. The second barge banked hard, left to escape. PT-48’s helmsman stayed on its tail. Harper closed to 600 yd. Horton emptied the second magazine, landing 22 hits. The barge’s armor held for the first five, but the sixth punched through. The seventh hit something flammable.

The barge exploded instantly in a massive fireball and ammo secondary and the hold disintegrated on the spot. The third and fourth barges scattered in panic, one towards Tsavo and the other toward Guadal Canal. PT-48 chased the one heading south. Horton loaded the third magazine. Due to thermal expansion, the rotating collar was starting to bind.

He had to put his whole weight into sloowing the gun to track the target. The bearing surface Thomas had ground was wearing down fast under the combat load. At 700 yards, Horton emptied the third magazine. The Japanese barge fired back frantically. 7.7 mm rounds rad the bow of PT-48. One bullet punched through the deck just 18 in from Horton’s leg. He didn’t stop.

The 37mm shells walked from the stern of the barge to the bow. The engine died and the barge drifted aimlessly as the soldiers abandoned ship. It didn’t sink immediately, but it was a total loss. At 12:20 a.m., PT-48 withdrew. Horton had fired 90 rounds. The gun hadn’t jammed, the mount hadn’t snapped, and the deck hadn’t collapsed.

The Japanese had lost two sunk and one crippled. The Americans had zero casualties. Harper sent a message to command with just one sentence. The modified aircraft gun is a success. The effect exceeded everyone’s expectations. By 3:00 a.m., every PT boat captain in Squadron 3 was demanding a gun, but Henderson Field only had 23 wrecks, and the squadron had 12 boats.

The math didn’t add up. By October 23rd, three more boats were equipped. The salvage operation became a streamlined process. The teams knew exactly which bolts to turn and which lines to cut. Removal time dropped from 90 minutes to 55. Mount designs evolved. After inspecting PT48’s original mount, Thomas found severe wear.

He scavenged bronze bushings from scrapped aircraft wheel hubs. These bushings drastically reduced friction, allowing the second generation mounts to rotate smoothly, even under heavy recoil. Ammo became the new bottleneck. The horseshoe magazines were designed for air combat, bursts of a few seconds, whereas sea battles lasted 20 minutes.

Horton had fired 90 rounds in his first fight. A boat carrying six magazines had only 180 rounds. It wasn’t enough. Ordinance men at the airfield began loading magazines around the clock. Each magazine had to be handloaded with 30 rounds. Even for an expert, it took 8 minutes. Four ordinance men worked shifts, producing 40 magazines a day.

Four boats on patrol needed 24 magazines each per night. The supply just barely met the demand. High explosive H rounds were death to the DHTsu barges. They were designed to destroy the aluminum and magnesium structures of aircraft. against one 4-in steel barge plating. They were overkill. A shell would blow a 12-in hole through the hull, and shrapnel would sweep the interior.

Two or three hits would disable a barge. Five to eight would sink it. On October 24th, PT40 engaged three barges in Kimbo Bay. The new M4 gun took out two of them within a single magazine. 20 seconds of fire, two ships ablaze, both sunk within 2 minutes. Although the third escaped in the dark, monitoring showed it was heavily damaged.

Squadron 3 realized the 37mm had completely rewritten the tactical playbook. Before they had to fire torpedoes blindly from 1,000 yd. Now they could charge to within 400 yd and sniping the targets. While being closer was more dangerous, it bypassed the persistent depth setting issues of the torpedoes. The Japanese commanders felt the threat immediately.

An intercept on October 25th showed barge crews reporting encounters with PT boats armed with heavy cannons and explosive shells. Some even used the term demon ships with aircraft guns. The psychological impact was massive. Japanese barges that previously moved with impunity were now being blown to splinters before they could deliver a single crate.

By November 1st, 1942, eight boats in Squadron 3 were armed. Every salvageable M4 cannon at Henderson had been stripped. A total of 21 guns were recovered, 17 mounted on boats, four kept as spares. The maintenance burden was significant. These were delicate aviation instruments intended to be pampered by ground crews.

On a PT boat, they were out at sea for days. Salt water corroded the hydraulic cylinders. Heat aged the seals and coral dust wore down the feed mechanisms. Gunner’s mates began teaching themselves field maintenance with improvised tools. Sergeant Walker was officially transferred to Tulagi in early November to oversee maintenance.

He set up a small workshop in a corrugated metal shack by the Wararf and taught a 3-day course to the crews. By mid- November, every boat had a dedicated specialist. South Pacific Command looked at the reports. Eight patrols, 23 barges engaged, 14 sunk, six damaged, and only three escaped. American PT boat losses, zero. The data was undeniable.

On November 18th, the modification report was sent to the Bureau of Ordinance in Washington. This secret document included blueprints, ammo data, and maintenance manuals. Despite the bureaucracy, the results were too good to ignore. On December 7th, 1942, the first anniversary of Pearl Harbor, the Bureau of Ordinance approved the mass production of standardized PT boat gun mounts.

The first 100 units were to be delivered in 90 days, but the front couldn’t wait 90 days. In mid December, Squadron 6 arrived at Tulagi. Their 12 boats were factory standard 50 cal machine guns and 20 mm Orlicans, but no 37mm cannons. They had intended to fight a torpedo war, but found squadron 3 having all the success with plane guns. The commanders demanded cannons, but the Henderson graveyard was empty.

The rescue came from New Calonia. A shipment of factory new M4 replacement guns had arrived. 12 of them still coated in factory grease. The PTBO commanders got creative. On paper, these guns were headed to the airfield for plane maintenance. In reality, they never made it. A PBY Catalina flew the guns directly to Tagi.

On December 20th, Squadron 6 was armed with brand new cannons. Compared to the salvaged Rex, these new guns had perfect hydraulics and flawless feeding. By January 1943, there were 24 boats armed with cannons in the Solomons. The Japanese supply line was facing systematic destruction. January’s combat reports showed 37 patrols, resulting in 41 sinkings and 19 damaged.

The cannon gave PT boats unprecedented offensive capability. And because of the range and power advantage, US losses plummeted. In the preceding months, they had lost six boats. After the cannons, they lost only two, and both were due to non-combat accidents. Tactics evolved further. PT boats began operating in hunter killer pairs.

One boat would use its 37mm as the primary attacker, while the other provided suppression with machine guns, keeping torpedoes ready for larger Japanese ships. This combo drastically increased survival rates. Crews learned that a barge usually required two or three magazines and began aiming for high value targets like fuel tanks and engine rooms.

The Japanese were forced to send destroyers to escort the barges. Faced with 5-in destroyer guns, the PT boats were once again outmatched. Some called for heavier 40mm or 3-in guns, but since structural changes were too slow, the Bureau of Ordinance chose to improve the ammo instead. Tungsten carbide armor-piercing rounds were sent to the front to deal with Japanese patrol craft.

Meanwhile, the factories in Rhode Island finished the mount production. Though 30 homemade mounts had already been welded at the front by the time the factory units arrived in March, the official versions were more stable and precise. Squadron 8 followed with standard cannon equipment to New Guinea.

There, the cannons were even more effective in narrow waterways and jungle cover, sinking over 60 barges in 3 months. The field had proven it. The modification was reliable and lethal. In June 1943, the Bureau of Ordinance finally released the naval version of the 37mm, the M9. It had a longer barrel, higher muzzle velocity, and was more durable.

The M9 weighed 405 lb, more than double the M4, and its muzzle velocity reached 3,000 ft per second. This extended the effective range to 1,000 yd, allowing PT boats to fire from outside the enemy’s return fire. In October, Squadron 15 was the first to re-equip with deck structures specifically reinforced for the M9.

Although it still used 30 round horseshoe magazines, the high chamber pressure meant ordinance men had to be meticulous about seating the rounds to prevent jams. By January 1944, the 37mm cannon was standard factory equipment for all American PT boats. Whether built by Elco or Higgins, the boats left the yard with reinforced gun mounts.

The journey from scavenging scrap to industrial standardization had taken 18 months. Later, commanders in the Mediterranean demanded the same upgrades to deal with German barges and Italian fast boats. The M9 performed just as brilliantly there. When the PT boats returned to the Philippines in October 1944, they were no longer just torpedo boats.

They were gunboats. Statistics from November were staggering. 36 boats destroyed 63 Japanese vessels with zero losses. The PT boat had transformed from a simple torpedo platform into a floating fortress of 37 mm guns, 40 mm guns, rockets, and machine guns. All of this began 2 years prior with a single salvaged gun on the PT48.

Colt produced 1,500 MM9 cannons in total. By early 1945, the Japanese barge supply system in the Philippines was paralyzed. It wasn’t that they didn’t want to send supplies. It was that the PT boats were sinking them faster than they could build them. The war ended on August 15th, 1945. Out of 531 PT boats that served in Wowat, 432 survived and nearly all were armed.

Postwar analysis showed that after the cannons were added, kill efficiency increased sixfold and casualty rates dropped by 60%. Their total count exceeded 800 ships sunk. This meant at least 48,000 Japanese soldiers and 6,000 tons of ammo never reached the battlefield. Vice Admiral Teo Karita later admitted that the Japanese lost 73% of their supply barges.

Soldier memoirs

Lieutenant Harper retired after the war with 19 kills and a Navy cross, returning to Philadelphia. Names like Walker, Thomas, and Horton are recorded in the archives. Though that crude, salvaged mount never received a medal, it changed the war. The success of the PT boat didn’t lie in its wooden hull or its engines, but in the ingenuity of a crew that dared to weld parts from a crashed airplane onto a boat and charge into battle.

If you watched until the end and this story moved you, please give us a like. Leave a comment saying, “I made it to the end.” Tell us where you’re from and share if anyone in your family served in Welderville, too. Subscribe and turn on notifications to help us keep these forgotten histories alive.

We bring you untold stories of history everyday.