Hiro G2H



As the Washington (Disarmament) Treaty of 1922 limited the tonnage for capital ships for the US Navy, the Royal Navy and the Japanese Navy, so did the London (Disarmament) Treaty of 1930 limit the number of smaller ships including aircraft carriers and cruisers. Japanese Navy planners recognized the capability of Navy land-based bombers that could be used to supplement and reinforce fleet activities and thus were responsible for the development of the Hiro Navy Type 95 Land-based Attack Aircraft.

To meet this new requirement for air power starting in 1932, Rear Admiral Isoroku Yamamoto, Chief of Engineering Department, Naval Air Headquarters, called for a land-based long-range attack bomber that could fly more than 2,000nm and carry two tons of bombs. The Hiro Arsenal was selected for the project, for at that time it was the most experienced in the design of all-metal large aircraft. Chief designer was Lieut-Cdr (Ordnance) Jun Okamura who had served in this capacity for the preceding Type 91 Flying-boat project. This land-based bomber became the primary concern at the Hiro Arsenal, diverting attention from the development of the flying-boats previously described.

At the start of the project, the prototype’s designation was the Hirosho 7-Shi Special Attack Aircraft, with the short designation G2HI. Structurally, it was a combination of a large wing of traditional Wagner diagonal tension-field structure and a slender fuselage of monocoque construction. The twin fins and rudders were similar to those of the final design of the Type 90-1 Flying-boats, and the ailerons were of the Junkers double-wing variety. One of the innovative features of the armament installation was a cylindrical belly gun turret which retracted into the fuselage. This feature was carried over into early versions of the Mitsubishi Navy Type 96 Land-based Attack Aircraft, that were code-named Nell by the Allies during the Pacific War.

To power the new bomber, two 900-1,180hp Type 94 water-cooled engines were selected, the most powerful aircraft engines available at that time. They were being developed by the Hiro Arsenal as a scaled-up version of the 600hp Type 90 Engine. It was felt that with these new engines, the aeroplane would be equivalent to a three- or four-engined aircraft of the time. Although the airframe dimension, wing area, and empty weight were almost identical to the Type 90-1 Flying-boat, aircraft range and payload were increased by nearly 50 percent. This was the largest land-based aeroplane in the Navy at that time, second only to the Army’s Type 92 Heavy Bomber (Ki.20) of the Junkers-G 38 design, yet it was the first of such a large size to be designed from the beginning as a land-based attack bomber. With two engines, its wing span was 103 ft 11 1/4in, marginally bigger than the four-engined Boeing B-17 Flying Fortress with 103ft 9in wingspan.

The first prototype was completed on 29 April, 1933, at the Hiro Arsenal and moved by ship to Yokosuka. There it made its first flight in mid-May 1933 in the presence of Rear Admiral Yamamoto who had originated this bomber concept for the Navy. Making the first flight were Lieut-Cdr Shinnosuke Muneyuki and Lieut-Cdr Toshihiko Odahara, both of the Flight Experiment Group of the Yokosuka Kokutai. After taking off, Muneyuki made one pass over the field for the spectators and proceeded to Kasumigaura Air Base where testing was to take place.

As flight evaluations continued, it was found that the aeroplane possessed outstanding performance as the Navy’s largest land-based aeroplane at that time. But shortcomings became evident, including tail vibrations caused by the light structure of the fuselage, aileron flutter, and unreliable engines. One aircraft was lost during test flying because of aileron and tail flutter, causing it to ditch in Tokyo Bay. Corrections were made to the design enough to justify production.

In June 1936, the aeroplane was officially accepted by the Navy as the Type 95 Land-based Attack Aircraft, at the same time as the Navy accepted the Type 96 Land-based Attack Aircraft (G3M 1), Nell. To avoid identity confusion between the two, the G3Ml was referred to as the Type 96 Chu-ko (Medium Attack) or simply ‘Chuko,’ while the G2H was called the Type 95 Dai-ko (Large Attack) or ‘Dai-ko.’

After six of the G2H bombers had been produced at Hiro Arsenal, production was transferred to Mitsubishi. Before long, however, the Navy asked that production be concentrated on the smaller G3M, curtailing the G2H because of maintenance difficulties with the Type 94 Engines and the aeroplane’s low-speed flying characteristics. Consequently, production ended with only two having been manufactured by Mitsubishi.

With the activation of the Kisarazu Kokutai on 1 April, 1936, all remaining G2H1s (a total of eight were built) were assigned to this unit but were regarded as second-line aircraft because of the better performance of the G3Ms.

Heavy losses were experienced by G3Ms over Nanjing in August 1937, resulting in the deployment of the G2Hs to an airfield on Saishuto Island (now Cheju Do, off the southern coast of South Korea), and while en route, and for unexplained reasons, one G2H dropped out of formation and crashed near the coast of Sagami Bay southwest of Tokyo. Once in place, and established as the 1st Combined Kokutai with other forces from Kanoya, they made their first mission into China in support of ground forces in the Shanghai area on 30 September, 1937, under the command of Lt Motokazu Mihara. They made further attacks against nine major combat areas and received considerable damage from AA fire but no aeroplanes were lost.

Disaster did catch up with these G2Hs on 24 October, 1937, when one aircraft caught fire while its engines were being started and soon exploded. The fire spread to the other G2Hs, each loaded with three 250kg, five 60kg and five 50kg bombs, exploding successively until four aircraft were destroyed and the fifth badly damaged.

Specifications (G2H1)
Twin-engined land-based mid-wing monoplane bomber. All-metal stressed skin construction.
Crew of seven.
Two 900-1, 180hp Hiro Type 94-1 eighteen-cylinder W-type water-cooled engines, driving four-bladed wooden propellers.
One nose-mounted flexible 7.7mm machine-gun, twin dorsal 7. 7mm machine-guns retractable turret-mounted, one retractable turret-mounted ventral 7.7mm machine-gun. Bomb load: six 250kg (551Ib) bombs or four 400kg (881Ib) bombs.
Span 31.68m (103ft 11 1/4in); length 20.15m (66ft 1 1/4in); height6.28m (20ft 7 1/4in); wing area 140sq m (1,506.996sq ft).
Empty weight 7,567kg (16,682Ib); loaded weight 11,000kg (24,250Ib); wing loading 78.5kg/sq m(16Ib/sq fr); powerloading 6.11 kg/hp (13.4lb/ hp).
Maximum speed 132kt (152mph) at 1,000m (3,280ft); cruising speed 90kt (104mph); climb to 3,000m (9 ,843ft) in 9min 30sec; service ceiling 5,130m (16,830ft); range 1,080 to 1,557nm (1,245 to 1,800sm).
Hirosho built six from 1933 and Mitsubishi built two from 1936.

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