Mitsubishi Type 1 Attack Bomber Hamaki / G4M Betty
Technical Information

Background
Designed and built by Mitsubishi for the Imperial Japanese Navy (IJN) designated Type 1 Attack bomber. In Japanese, 一式陸上攻撃機, 一式陸攻 Isshiki rikujō kōgeki ki, Isshikirikkō. Japanese crews nicknamed it Hamaki (Cigar) due to the cylindrical shape of the fuselage. Allied code name "Betty".

The Betty redefined Naval bomber operations because of its extremely long range. By comparison, RAF crews struggled 900 miles to Germany, while Japanese Navy crews hauled similar bomb loads to targets twice as far away in their spacious, well equipped Betty bombers, making it one of the outstanding bombers of the era. The Betty's main weakness was its large unprotected fuel tanks. If hit, bomber had a tendency to catch fire or explode. Later, attempts were made to add fuel tank protection by adding material to the exterior.

The tail position was armed with a 20mm cannon Type 99 flexible cannon type 1 (99 Shiki 20mm Senkai-kiju 1gata). The weapon had a circular drum magazine with 45 rounds that weighed 16.5 kg (36.38 pounds). Alternately, there was a smaller circular drum magazine with 30 rounds that weighed less.

Model 11
The first bomber model of series, with 1,140 kW (1,530 hp) Mitsubishi MK4A Kasei Model 11 engines driving three-blade propellers. The following modifications were made during production.

Model 12
The Model 12 was possibly an interim model or designation that ultimately ceased being used. The Model 12 is cited in Japanese plan for production aircraft, September 1943 from plant Suzuka, yet in October 1943 they delivered only the Model 11.

G4M2 Model 22
The first prototype was completed by November 1942 and made a first flight in December 1942.

G6M1-L Betty (Transport Version)
The G6M1-L Betty was a transport version of the Type 1 / G4M1 Betty. This variant had several differences, including lack of a middle row of windows on the sides of the nose. The pitot tube was more forward on the nose. The waist blister were nearer to the wing and struts different. The position of the antennas on the top of the fuselage was different and this model lacked a loop antenna. The fuselage door was oval shaped and the type lacked defensive armament or ordnance.

Production
A total of 2,446 Bettys were built.

References
Air'Tell Research Report "G4M Serial Numbers" by Jim Long
Thanks to Yoji Sakaida, Jim Long and Richard Dunn for additional information

Technical Details (Type 1 Model 22 / G4M2)
Crew  7-10 (pilot, co-pilot, navigator, mechanic, gunner, gunner, gunner)
Engine  2 x Mitsubishi MK4P Kasei 21 fourteen-cylinder air-cooled propellers (G4M2)
Span  25m
Length  20m
Height  6m
Maximum Speed  236 km/h
Range  3,270 miles
Armament  (nose, turret, waist) 7.7mm machine guns (tail) 20mm cannon
Bomb load  1 x 800 kg aerial torpedo or up to 1,000 kg of bombs