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Mitsubishi G4M Betty

Mitsubishi · Land-Based Torpedo Bomber / Medium Bomber / Torpedo Bombing / Long-Range Maritime Strike · Japan · WWII (1939–1945)

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The Mitsubishi G4M (Allied reporting name Betty) was an Imperial Japanese Navy twin-engine medium bomber + torpedo bomber — the principal IJN long-range bomber of WWII + one of the most-large Japanese WWII bombers. Kiro Honjo designed the G4M at Mitsubishi in 1937-1939; the prototype first flew on 23 October 1939. About 2,435 G4Ms were built between 1940 and 1945 at Mitsubishi Nagoya. The aircraft served IJN throughout WWII Pacific + Southeast Asian + Pacific Home Defence theatres 1941-1945.

The G4M2 (most-numerous variant) used 2 × Mitsubishi Kasei MK4P 14-cylinder radial engines (1,800 hp each). Maximum speed 437 km/h, range 6,000 km (with reduced bomb load), service ceiling 8,950 m. Armament: 1 × Type 91 800 kg torpedo or 1,000 kg of bombs + 4 × 7.7 mm + 1 × 20 mm machine guns / cannon. Crew: 7. The aircraft's defining feature was its exceptional range — 6,000 km gave the G4M reach across the entire Pacific theatre that no Allied medium bomber could match. The principal weakness was poor crew + fuel-tank protection — Allied pilots called the G4M "the flying lighter" because the unprotected wing fuel tanks ignited easily under fighter attack.

G4M service was central to Japanese WWII operations. Combat use included Malaya invasion 1941 (sank HMS Prince of Wales + HMS Repulse 10 December 1941 — the first capital warships sunk by aerial torpedo attack while at sea), Pearl Harbor reconnaissance + follow-up strikes, Solomon Islands campaigns 1942-1943, and Pacific Home Defence late war. About 1 G4M airframe (with components from multiple aircraft) is being restored at the Planes of Fame Museum, California; otherwise no G4Ms survive complete.

For Kids — a shorter, friendlier version

The Mitsubishi G4M Betty was Japan's main long-range bomber in World War II. The G4M first flew in 1939 and entered service in 1941. Allied pilots called it the "Betty" — the Allied naming convention used girls' names for Japanese bombers.

The G4M is about 64 feet long — longer than a school bus. Two Mitsubishi Kasei radial engines (1,800 hp each). Top speed 282 mph. The G4M had amazing range — about 3,200 miles — but at a deadly cost: no armor for the crew, no self-sealing fuel tanks. Allied pilots nicknamed the G4M the "Flying Cigar" because its slim shape and the way it caught fire when hit.

About 2,435 G4Ms were built between 1939 and 1944. They fought everywhere in the Pacific — bombing Allied bases, attacking ships, and dropping mines. The most-famous G4M mission was attacking British battleships Prince of Wales and Repulse on December 10, 1941 (3 days after Pearl Harbor). G4Ms sank both ships, killing 840 British sailors — the first time battleships were sunk by aircraft while at sea.

The G4M's weakness — no armor and explosive fuel tanks — was deadly. Many G4M crews were lost. By 1944 the G4M was hopelessly outclassed by Allied fighters. Japan kept building them anyway because they had no better airplane. About 1-2 G4Ms survive in museums today, all heavily damaged.

Fun Facts

Allied pilots called the G4M the "Betty" or the "Flying Cigar."
About 2,435 G4Ms were built between 1939 and 1944.
G4Ms had no armor for the crew and no self-sealing fuel tanks — making them dangerous to fly.
G4Ms sank the British battleships Prince of Wales and Repulse on December 10, 1941.
The G4M had amazing range — about 3,200 miles on one tank of fuel.
Top speed 282 mph — slow by 1942 standards.
Only 1-2 G4Ms survive today, all heavily damaged.

Kids’ Questions

How did the G4M sink two British battleships?

On December 10, 1941, Britain sent battleships Prince of Wales and Repulse with no air cover to fight the Japanese invasion of Malaya. Japanese G4M and G3M bombers (about 85 total) found them and attacked. The Japanese used a coordinated mix of torpedoes (G4Ms dropping torpedoes from low altitude) and bombs (G3Ms dropping from higher altitude). Without their own fighters to protect them, the British battleships couldn't defend against air attack from multiple angles. Both ships sank within hours. 840 British sailors were lost. The battle proved that battleships couldn't survive without air cover — changing naval warfare forever.

What was kamikaze?

Kamikaze (Japanese for "divine wind") was the Japanese military's deliberate use of pilots crashing their airplanes into enemy ships as a final desperate weapon. Starting in October 1944, when Japan was clearly losing the war, kamikaze pilots became more common. They would load their airplanes with bombs and fly directly at American ships, attempting to hit and sink them. About 3,800 kamikaze attacks were launched by Japan in WWII. They damaged or sank about 90 American ships. Many old G4Ms (and other older Japanese aircraft) were used as kamikaze airplanes in the war's closing months — pilots barely trained, airplanes barely flyable, but deadly when they hit their targets.

Variants

G4M1 (early): Initial production. About 1,200 built.
G4M2 (refined): Improved Kasei-engined variant. About 1,200 built.
G4M3 (final): Final variant with improved fuel-tank protection. About 35 built.

Notable Operators

Imperial Japanese Navy (1941-1945): Sole operator. Pacific + Southeast Asian theatres + Home Defence.

Frequently Asked Questions

Did G4Ms sink the Prince of Wales?

Yes. On 10 December 1941, IJN G4M1 + Mitsubishi G3M Nell torpedo bombers attacked Royal Navy Force Z (HMS Prince of Wales battleship + HMS Repulse battlecruiser) off the coast of Kuantan, Malaya. About 50 G4Ms + G3Ms delivered torpedo attacks that sank both capital ships in ~80 minutes — the first capital warships sunk by aerial torpedo attack while at sea + a turning point in naval doctrine that demonstrated battleships were vulnerable to land-based bombers without air cover. The action effectively ended the era of battleships' dominance in naval warfare.

Why was the G4M called the flying lighter?

Poor fuel-tank + crew protection. The G4M's wing-mounted fuel tanks were unarmoured + uninsulated — Allied incendiary rounds easily ignited the gasoline + caused catastrophic fuel-fire losses. Japanese designers prioritised range over survivability — the 6,000 km range required maximum fuel capacity + minimum weight, sacrificing armour. Allied pilots noted that even minor fighter-fire damage often caused G4Ms to burst into flames; the nickname "flying lighter" + "one-shot lighter" became standard Allied references to the type.

Sources

Wikipedia — Mitsubishi G4M