Mitsubishi G4M
The Mitsubishi G4M was a twin-engine, land-based medium bomber flown by the Imperial Japanese Navy Air Service through the Second World War. The Allies called it the "Betty" and its own crews called it "Hamaki" (cigar), after its round fuselage. It was built for extreme range, which it achieved with unprotected wing fuel tanks and no crew armor, and it became the most produced Japanese bomber of the war — and, once Allied fighters could reach it in numbers, one of the most flammable.
Why It Mattered
The Mitsubishi G4M was the Imperial Japanese Navy's main land-based bomber of the Second World War, and Japan built more of them than any other bomber of the war. The Allies called it the "Betty"; its own crews called it "Hamaki", Japanese for cigar, after its round fuselage. From the first day of the war until after the surrender, it served across the Pacific and Indian Oceans. Its long range let it reach targets other land-based bombers could not, but the weight saved to gain that range left it with unprotected fuel tanks and no armor, and once Allied fighters could intercept it in numbers it burned readily — the Allies nicknamed it the "flying lighter".
Design Notes
The G4M began with a 1937 Navy specification for a replacement for the Mitsubishi G3M (Allied codename "Nell"): a twin-engine, land-based attack bomber that had to cover 4,722 km (2,933 miles) carrying no torpedo or bomb load of the same weight, at a top speed of 398 kph (247 mph). A Mitsubishi design team led by Kiro Honjo met the range demand by carrying fuel in wing tanks that were not resistant to explosion when punctured; the heavier, safer self-sealing tanks, the team judged, would have made the required range impossible. The fuselage was streamlined but rotund, enclosing a bomb bay and room for a crew of seven to nine to move about, and about half the crew manned defensive guns: 7.7 mm machine guns in the nose, upper fuselage and sides, and a 20 mm cannon in the tail. Crew armor was left out for the same reason the protected tanks were: protection was sacrificed to the Navy's demand for range.
Operational History
The prototype was dismantled, carted 48 km (30 miles) on five ox-drawn farm carts to Kagamigahara airfield — Mitsubishi's Nagoya plant had no airstrip of its own — reassembled there, and flown by test pilot Katsuzo Shima on 23 October 1939. The Navy then shelved the bomber in favour of the G6M1, a more heavily armed variant meant to escort other bombers; when that diversion failed to live up to expectations, the G4M1 was ordered into production, and the first production aircraft rolled off the line in April 1941. In its first year of combat the type devastated Clark Field in the Philippines on 8 December 1941 and took part in sinking the British battleship Prince of Wales and battlecruiser Repulse two days later. Its crews attacked targets from the Aleutians to Australia, and against limited fighter opposition the missing armor and self-sealing tanks were no hindrance. That changed as Allied fighter strength grew: on 18 April 1943, U.S. Army Air Corps P-38 Lightnings intercepted the two Bettys carrying Admiral Isoroku Yamamoto, the architect of the Pearl Harbor attack, and his staff, and destroyed both. Mitsubishi kept revising the design rather than replacing it; the G4M Model 34 added self-sealing tanks of about a third less capacity, armor at all crew positions and a redesigned tail turret, while another variant became the mother ship that carried the Kugisho Ohka piloted bomb. Mitsubishi produced 2,414 G4Ms in all, and four days after the war ended on 15 August 1945, two Bettys painted white overall with green crosses landed at Ie Shima carrying the Japanese surrender delegation, which had boarded in Kyushu on its way to the Philippines.
Afterlife
No G4M survives fully intact, and none flies. The best-preserved remains are held by the Smithsonian's National Air and Space Museum: the forward fuselage of a G4M3 Model 34, brought to the United States along with 145 other Japanese aircraft selected for test and evaluation, flight-tested as T2-2205 and later dismembered with a cutting torch for reasons not recorded; the museum keeps it in storage rather than on display. The most complete airframe, a G4M1 recovered from Babo airfield, was sold to the Planes of Fame Air Museum in Chino and displayed there unrestored in a crash diorama until November 2015, when the Flying Heritage and Combat Armor Museum in Everett, Washington, bought it; it has remained in storage to the present day. A restored G4M2 fuselage is on display at the Kawaguchiko Motor Museum in Japan. The wreck of Yamamoto's G4M1 still lies at the crash site in the jungle near Panguna, Bougainville Island, with parts and artifacts from it displayed at museums in Papua New Guinea, Australia and Japan.