Jaw-Dropping WWII Fact: How America’s B-25 Bomber Became a Destroyer-Killer with a Hand-Loaded 75mm Cannon—Sinking a Japanese Warship in 5 Shots and Setting the Stage for Future Gunships

When we think of World War II’s iconic aircraft, images of streamlined fighters and graceful bombers come to mind—but one of the most jaw-dropping chapters in aviation history belongs to an unlikely “bomber turned destroyer-killer.” In a stunning display of innovation under fire, U.S. engineers transformed the North American B-25 Mitchell medium bomber into a flying tank, fitting it with a hand-loaded 75mm cannon—at that time, the largest gun ever installed in an operational Allied aircraft.

The B-25’s audacious transformation paid off in spectacular ways, including an episode when one of these cannon-armed bombers sank a Japanese destroyer escort with just five shells. The story not only redefined what tactical bombers could achieve on the battlefield but also set the standard for future gunship innovations like the legendary AC-130.

From Medium Bomber to Gunship: The Genesis of a Bold Idea

The B-25 Mitchell had already earned its place in history, famously launching the Doolittle Raid in 1942 and proving itself a reliable, versatile attack bomber across multiple theaters of war. But by the latter half of the conflict, the U.S. Army Air Forces were facing new and evolving threats in the Pacific—namely, heavily armed Japanese ships that posed a dire risk to Allied naval and amphibious operations.

Conventional bombing was effective, but it often demanded large formations and exposed aircraft to punishing anti-aircraft fire. A solution was needed that could deliver devastating, pinpoint attacks from a safer distance. Drawing inspiration from earlier experiments and desperate to enhance maritime strike capabilities, U.S. engineers proposed something unprecedented: arming the B-25 with a tank-busting 75mm M4 cannon—the main armament from the M4 Sherman medium tank.

Engineering Feat: Mounting the “Flying Artillery”

Fitting a howitzer into an airplane presented daunting challenges. The massive gun, weighing over 900 pounds (roughly 400 kg), was shoehorned into the nose of specially-built B-25G and B-25H models. Engineers devised a hand-loading system: after each shot, a crew member would wrestle a 15-inch shell into the breech—a process demanding both muscle and nerves of steel.

Modifications also included reinforced airframes to handle the cannon’s tremendous recoil and redesigned cockpit layouts. To complement the 75mm “main gun,” these B-25 variants bristled with .50-caliber machine guns on either side of the nose, forming a deadly forward battery. As a result, B-25 pilots could first rake enemy ships with machine gun fire—the gun flashes serving to mask the opening of the cannon’s breech and give the loader time to reload.

Test-firing the system was dramatic: the gun’s blast jolted the entire aircraft and filled the cockpit with acrid smoke, while spent shell casings tumbled noisily across the floor. But the results proved promising—the cannon’s shells could punch through the armored decks and thin hulls of destroyers, transports, and even coastal bunkers from several thousand feet away.

Combat Debut: The B-25G and B-25H Take On Japanese Shipping

B-25s armed with the 75mm cannon flew their first operational missions in the South Pacific in 1943. Under the control of the Fifth Air Force and legendary “Sea Wolf” pilots like Major Paul “Pappy” Gunn, these aircraft began prowling the shipping lanes off New Guinea and the Philippines, hunting for enemy convoys and warships.

Attacks often began with a low-level run over the water. Pilots and bombardiers coordinated tightly, lining up to fire the 75mm cannon at the vulnerable amidships or stern sections of enemy ships. After each shot, the loader would slam another round into the breech, and the process would repeat—often under withering anti-aircraft fire from the decks below.

One of the most celebrated episodes came when a B-25, during an anti-shipping raid in 1944, engaged a Japanese destroyer-escort. The bomber’s first shot crippled the ship’s bridge; the second and third penetrated the hull. By the fifth round, the destroyer was listing heavily and ultimately capsized—sunk almost single-handedly by a bomber-turned-gunship. The feat stunned both Allied and Axis observers and marked a new pinnacle for precision air-to-surface firepower.

The Largest Aircraft Gun of Its Era

The 75mm gun on the B-25 was, for several years, the largest weapon ever fitted to a production combat aircraft. Its destructive power dwarfed most anti-tank and anti-material guns then in use by Allied or Axis air forces. Not surprisingly, the concept was both celebrated and controversial: while its psychological impact and ability to destroy enemy ships were undeniable, the process of hand-loading meant such bombers could typically fire only four to five shells in a single attack pass.

Still, U.S. air crews adapted impressively, refining their attack runs and developing new tactics to maximize their firepower and minimize exposure. In many cases, a few well-placed shots from the B-25’s cannon could send entire convoys into panic—or prevent enemy troop reinforcements from ever reaching contested beaches.

Legacy: Paving the Way for Future Gunships

The B-25’s cannon variants eventually gave way to multi-gunned attack planes and, ultimately, rocket-armed strike aircraft as the war’s requirements evolved. And yet, the daring experiment of turning a medium bomber into a ship-killing “flying artillery piece” resonated well beyond World War II.

Decades later, the U.S. Air Force took direct inspiration from these B-25s when developing the legendary AC-130 gunship—an aircraft famous for mounting even larger cannons, including its own 105mm field howitzer, and capable of circling over battlefields while delivering relentless firepower.

A Forgotten Marvel Revisited

Today, the story of the cannon-equipped B-25 is a testament to American ingenuity, improvisation, and the relentless search for battlefield solutions in the fog of war. It’s a tale that reminds us how warfare—and victory—often rely on the courage to do what seems impossible: like firing a tank cannon from the nose of a bomber at Japanese destroyers thousands of miles from home.

The legacy of the “flying fortress with a tank gun” endures not just in museums, but in every gunship that circles the skies—from the WWII B-25G and B-25H to the mighty AC-130s that patrol modern battlefields today. Bound by daring, muscle, and raw firepower, this jaw-dropping chapter in aviation continues to inspire awe in all who discover it.