The Mitsubishi G4M was a twin-engine, land-based medium bomber formerly manufactured by the Mitsubishi Aircraft Company, a part of Mitsubishi Heavy Industries, and operated by the Imperial Japanese Navy from 1940 to 1945.
Its official designation is Mitsubishi Navy Type 1 attack bomber and was commonly referred to by Japanese Navy pilots as Hamaki due to the cylindrical shape of its fuselage.
Designed to a strict specification to succeed the Mitsubishi G3M already in service, the G4M boasted very good performance and excellent range and was considered the best land-based naval bomber at the time.
This was achieved by its structural lightness and an almost total lack of protection for the crew, with no armour plating or self-sealing fuel tanks.
The G4M was officially adopted on 2 April 1941 but the aforementioned problems would prove to be a severe drawback, often suffering heavy losses; Allied fighter pilots nicknamed the G4M “The Flying Lighter” as it was extremely prone to ignition after a few hits.
It was not until later variants of the G4M2 and G4M3 that self-sealing fuel tanks, armour protection for the crew and better defensive armament was installed.
Nevertheless, the G4M would become the Navy’s primary land-based bomber.
It is the most widely produced and most famous bomber operated by the Japanese during World War II, and it served in nearly all battles during the Pacific War.
The aircraft is also known for being the mothership that carried the Yokosuka MXY-7 Ohka, a purpose-built anti-ship suicide weapon during the final years of the war.
Of the 2,435 G4Ms produced, no intact aircraft have survived.
The G4Ms predecessor the Mitsubishi G3M went into service in 1937 in China.
Only two months later the Japanese Navy issued specifications to Mitsubishi.
The specifications, unprecedented at the time, called for a twin-engine, land-based, attack bomber with a top speed of 398 kilometres per hour (247 mph), altitude of 3,000 metres (9,800 ft), and a range of 4,722 kilometres (2,934 mi) unloaded (without bombs and torpedoes), and a range of 3,700 kilometres (2,300 mi) when carrying an 800 kilograms (1,800 lb) torpedo or the same weight in bombs.
The G4M was designed for a long range and high speed at the time of its introduction.
In order to meet the Navy’s specifications a Mitsubishi team led by Kiro Honjo did not incorporate self-sealing fuel tanks and armour plating to save weight and extend range.
This consequently made both the G4M and the Zero, in which Mitsubishi used the same design features, vulnerable to machine gun and cannon fire.
The pilots of the Imperial Japanese Navy called the G4M the “hamaki” (“cigar”), although this was due to its shape.
Due to deficiencies of the G3M in warding off concentrated fighter attacks Honjo incorporated 7.7 mm (0.30 in) guns in the nose, on top and both sides of the fuselage and in the tail a 20 mm (0.79 in) cannon was added.
When used for medium to high-altitude bombing against stationary land targets like supply depots, seaports or airfields, it was much harder to intercept.
Using its long range and high speed, the G4M could appear from any direction, and then it could be gone before any fighters intercepted them.
The 20 mm cannon in its tail turret was much heavier armament than was commonly carried by bombers of either side, making aerial attacks from the rear quite dangerous for the Allied fighter aircraft.
Sometimes, if they did not catch fire after being hit in the wings by flak from the ground or by machine gun bullets from enemy fighters, G4Ms also proved to be able to remain airborne despite being badly damaged.
For example, after the attack of the 751 Kōkūtai (air group) on the USS Chicago during the Battle of Rennell Island, three out of four surviving aircraft (of the original eleven) returned despite flying with only one engine.
As the war continued improved bomber designs failed to materialize and Mitsubishi began creating additional versions to fulfill various new missions as well as eliminate the weakness in the design including various engine and weapon variants.
The G4M2 redesign failed to rectify the G4M’s vulnerability to weapons fire.
Variants
G4M1
G4M1 prototypes
(Mitsubishi Navy Type 1 attack bomber) / (Mitsubishi Navy Experimental 12-Shi land attacker).
Two prototypes built.
G4M1 Model 11
(Mitsubishi Navy Type 1 Attack Bomber 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
March 1942
The first aircraft (241st production example) fitted with Mitsubishi MK4E “Kasei” Model 15 engines with larger superchargers for better high-altitude performance, became standard in August 1942 from 406th aircraft onwards.
These MK4E-engined aircraft have often (erroneously) been referred as the “G4M1 Model 12”.
Summer 1942
Propeller spinners introduced
March 1943
From 663rd machine onwards, 30 mm (1.181 in) rubber ply sheets installed beneath the wing outer surfaces to protect the underside of the fuel tanks (speed reduced by 9 km/h (4.9 kn; 5.6 mph) and range by 315 km (170 nmi; 196 mi), 5 mm (0.197 in) armour plates added into tail gunner’s compartment.
Spring 1943
Outer half of the tail cone cut away in order to improve tail gunner’s field of fire.
August 1943
A completely redesigned tail cone, with reduced framing and wide V-shaped cut out; this form of tail cone was also used in all G4M2 models.
September 1943
Individual exhaust stacks from 954th airframe onwards
Production of the G4M1 ended in January 1944.
G4M2
The first of the four G4M2 prototypes flew in December 1942 (
Mitsubishi Navy Type 1 Attack Bomber Model 22).
It differed from the preceding model in having Mitsubishi MK4P “Kasei” Model 21 engines with VDM electric four-blade propellers capable of full feathering function, redesigned main wings with LB type laminar flow airfoil and widened tail horizontal stabilizer wing area, which improved service ceiling to 8,950 m (29,360 ft) and maximum speed to 437 km/h (236 kn; 272 mph).
Main wing fuel tanks were enlarged to 6,490 l (1,710 US gal; 1,430 imp gal) which increased the range to 6,000 km (3,200 nmi; 3,700 mi) (overloaded, one way).
An electrically powered dorsal turret featuring a 20 mm (0.787 in) Type 99 cannon was introduced in place of G4M1’s dorsal position with a 7.7 mm (0.303 in) Type 92 machine gun, total guns armed were two 20 mm (0.787 in) Type 99 cannons (one tail turret, one top turret), and four 7.7 mm (0.303 in) Type 92 machine guns (one nose, two waists, and one cockpit side).
External differences also included increased nose glazing, flush side gun positions instead of blisters, and rounded tips of wings and tail surfaces.
These major improvements also made it possible for the G4M2 to carry more powerful bombs; one 1,055 kg (2,326 lb) Navy Type 91 Kai-7 aerial torpedo or one 800 kg (1,800 lb) bomb or two 500 kg (1,100 lb) bombs or one 800 kg (1,800 lb) Type 3 No. 31 bomb (ray-detective type bomb) and twelve 60 kg (130 lb) bombs.
The G4M2 entered service in mid-1943.
G4M2 Model 22
(Mitsubishi Navy Type 1 Attack Bomber Model 22)
The base model, the first production example completed in July 1943.
Introduced bulged bomb bay doors from 65th aircraft onwards, and an optically flat panel in the nose cone from the 105th aircraft onwards.
G4M2 Model 22Ko
(Mitsubishi Navy Type 1 Attack Bomber Model 22 Ko)
Very similar to previous model.
Carried Type 3 Ku Mark 6 search radar and was armed with 20 mm (0.787 in) Type 99 Model 1 cannons replacing the 7.7 mm (0.303 in) Type 92 machine guns in the lateral positions.
G4M2 Model 22 Otsu
(Mitsubishi Navy Type 1 Attack Bomber Model 22 Otsu)
Dorsal turret cannon changed to longer-barrelled 20 mm (0.787 in) Type 99 Model 2 cannon.
With bulged bomb bay doors as standard for larger bomb capacity.
Externally distinguishable from the Model 22 by a carburettor air intake on the top of the engine cowling.
G4M2a Model 24 Ko
(Mitsubishi Navy Type 1 Attack Bomber Model 24 Ko)
Armament similar to Model 22 Ko.
G4M2a Model 24 Otsu
(Mitsubishi Navy Type 1 Attack Bomber Model 24 Otsu)
Armament similar to Model 22 Otsu.
G4M2a Model 24 Hei
(Mitsubishi Navy Type 1 Attack Bomber Model 24 Hei)
Modified 24 Otsu, with one 13.2 mm (0.520 in) Type 2 machine gun mounted in tip of the nose cone, radar antenna relocated from that position to above the nose cone.
G4M2b Model 25
(Mitsubishi Navy Type 1 Attack Bomber Model 25)
One G4M2a modified to Mitsubishi MK4T-B Kasei 25 Otsu 1,360 kW (1,820 hp) engines, Only experimental.
G4M2c Model 26
(Mitsubishi Navy Type 1 Attack Bomber Model 26)
Two G4M2as modified to Mitsubishi MK4T-B Ru Kasei 25b 1,360 kW (1,820 hp) engines with turbochargers.
G4M2d Model 27
(Mitsubishi Navy Type 1 Attack Bomber Model 27)
One G4M2 modified to Mitsubishi MK4V Kasei 27 1,340 kW (1,800 hp) engines.
G4M2e Model 24 Tei
(Mitsubishi Navy Type 1 Attack Bomber Model 24 Tei)
Special version for the transport of the ramming attack bomb plane Kugisho/Yokosuka MXY-7 Ohka (“Baka”) Model 11, conversions of G4M2a Model 24 Otsu and 24 Hei.
Had armour protection for the pilots and fuselage fuel tanks.
MXY11
(Yokosuka Navy Type 1 attack bomber ground decoy)
Ground decoy non-flying replica of Mitsubishi G4M2 developed by Yokosuka
G4M3
G4M3 Model 34
(Mitsubishi Navy Type 1 Attack Bomber Model 34 Tei)
Redesigned G4M2 with added self-sealing fuel tanks, improved armour protection and an entirely new tail gunner’s compartment similar to that of late model B-26 Marauders.
Wings were also redesigned, and the horizontal tail plane was given dihedral.
Armed with two 7.7 mm (0.303 in) Type 92 machine guns in nose cabin and in both side positions, and one 20 mm (0.787 in) Type 99 Model 1 cannon in dorsal turret and tail.
Entered production in October 1944 in G4M3a Model 34 Ko form with 20 mm (0.787 in) Type 99 cannon inside positions instead of machine guns.
G4M3a Model 34 Hei
(Mitsubishi Navy Type 1 Attack Bomber Model 34 Hei)
Similar modifications as in corresponding Model 24 variants.
G4M3a Model 34 Otsu
(Mitsubishi Navy Type 1 Attack Bomber Model 34 Otsu)
Similar modifications as in corresponding Model 24 variants.
G4M3 Model 36
(Mitsubishi Navy Type 1 Attack Bomber Model 36) prototype.
Two G4M2 Model 34 modified to Mitsubishi MK4-T Kasei 25b Ru 1,360 kW (1,820 hp) engines.
G6M1
(Mitsubishi Navy Type 1 wingtip convoy fighter)
Initial model of the series, armed with three 20 mm (0.787 in) Type 99 cannon
(two in a belly blister, one in the tail) and one 7.7 mm (0.303 in) Type 92 machine gun in the nose, 30 built.
G6M1-K
(Mitsubishi Navy Type 1 large land trainer)
Trainers converted from G6M1s.
G6M1-L2
(Mitsubishi Navy Type 1 transport)
G6M1s modified as transports.
Specifications
Crew
7
Length
19.97 m (65 ft 6 in)
Wingspan
24.89 m (81 ft 8 in)
Height
4.9 m (16 ft 1 in) in rigging position
Wing area
78.125 m2 (840.93 sq ft)
Airfoil
Root
MAC118 mod (12.5%)
Tip
MAC118 mod (10%)
Empty weight
6,741 kg (14,861 lb)
Gross weight
9,500 kg (20,944 lb)
Max take-off weight
12,860 kg (28,351 lb)
Powerplant
2 × Mitsubishi MK4A Kasei 11,
14-cylinder air-cooled radial piston engines,
1,140 kW (1,530 hp) each for take-off
1,050 kW (1,410 hp) at 2,000 m (6,562 ft)
1,000 kW (1,340 hp) at 4,000 m (13,123 ft)
Propellers
3-bladed Hamilton Standard licensed Sumitomo constant speed variable-pitch
Performance
Maximum speed
428 km/h (266 mph, 231 kn) at 4,200 m (13,780 ft)
Cruise speed
315 km/h (196 mph, 170 kn) at 3,000 m (9,843 ft)
Stall speed
120 km/h (75 mph, 65 kn)
Range
2,852 km (1,772 mi, 1,540 nmi)
Ferry range
5,040 km (3,130 mi, 2,720 nmi)
Rate of climb
9.166 m/s (1,804.3 ft/min)
Armament
Guns
1× 20 mm Type 99 cannon (tail turret),
4× 7.7 mm Type 92 machine gun
(Nose turret ×1, waist positions ×2, top turret ×1)
Bombs
1× 858 kg (1,892 lb) Type 91 Kai-3 (improved model 3) aerial torpedo
Or
1× 800 kg (1,764 lb) bomb or 4× 250 kg (551 lb) bombs.
