19 October 2022
Graham Caldwell take a look at the Japanese self-propelled gun from WWII.
Funding for the pre-WWII expansion of the Japanese military prioritised the Imperial Navy and Air Forces, predominantly aircraft carriers and their inherent air components, plus building the world’s largest submarines. The Imperial Army was far less mechanised than Europe or America and by 1943 it still relied mainly on horse-drawn power to transport artillery in support of the infantry. This was a period when the M4 Sherman tank first appeared in the Pacific theatre and their forces suddenly woke up to the fact that they had no comparable tank to match it. By 1944 Japan had lost the initiative at sea and was faced with invasion of outlying island possessions. It was only now that Japanese Imperial Headquarters reallocated funding priorities, one of which was to begin producing self-propelled guns (SPG) to support the infantry formations, but with the added proviso to also have the capability to destroy Sherman tanks. However so much time and opportunity had been wasted that the economy was now experiencing acute shortages of raw materials, particularly steel. This explains why so few self-propelled guns were ever made by Japan in time to make any impact during the war.
Japanese Imperial Headquarters, in close liaison with Axis partner Germany, realised back in 1941 that its reliance on towed artillery in support of infantry was not keeping up with modern battlefield mobility. Nor had it a tank suitable to take on even the next generation of Western armoured fighting vehicles, even pre-Sherman. Needing to combine these two requirements, and because the Japanese Type 97 main battle tank and its later variants had become severely outclassed, a fast method to produce an up-gunned self-propelled gun was urgently required.
Left: A side view of the Type 1 Ho-Ni II SPG
To understand the development of the Type 1 Ho-Ni II SPG, which was not operational until 1943, you have to go back to 1941 and its earlier sister variant, the Type 1 Ho-Ni I SPG/tank destroyer. Expediency demanded retaining the Type 97 medium tank chassis and power pack, removing the turret structure and fixing in its place a 75mm Type 90 field gun, with a range of 12,000m (7½ miles) in an open air structure similar to the German Sd.Kfz 135 (Marder I). This saved weight and provided the necessary workspace for the gunnery crew, who were protected by a front and two-sided 51cm thick shield, but were totally unprotected from the rear. In order to make space for up to 54 rounds of ammunition the close-protection hull machine gun was removed and not replaced elsewhere. The first conversion prototype was trailed in June 1941, but lack of resources delayed its introduction until 1942. Only 26 Ho-Ni I units were produced, a few of which were assigned to the 2nd Mobile Artillery Regiment of the Japanese 2nd Tank Division during the Battle of Luzon for the 1944-45 Philippine’s campaign, but by this period the improved Type 1 Ho-Ni II SPG was coming on stream.
Type 1 Ho-Ni II SPG
The Ho-Ni II was an improvement over the Ho-Ni I, but because its principle role was to provide mobile artillery support for infantry and thus not designed as a tank destroyer, the Ho-Ni I 75mm gun was replaced with the 105mm Type 91 Army anti-tank howitzer in a modified open casemate. This required some amendments to be made because of stability issues with the much heavier main gun, which was fitted without an undercarriage, bolted and welded over a new support. ‘Type 1’ designation relates to the year ‘1941’ and ‘Ho-Ni II’ was Japanese abbreviated nomenclature meaning ‘gun fourth 2’. Because it was expected to fire mostly from shelters, some sources claim the three-panel shield thickness was reduced to 41cm, but most surviving specifications indicate that the 51cm thickness was retained and that the side armour was given re-positioned observation visors. As with its predecessor, the hull machine gun was removed to store extra rounds of the bulky two-part HE ammunition, plus it had two racks located inside the shield to hold a few shells in readiness. The main gun could traverse 10ᵒ to each side, but due to the recoil of the howitzer, combined with the large length of the back trunk, its elevation was poor and did not exceed 22ᵒ.
Left: Taking crew photographs in front of two Type 1 Ho-Ni I SPG’s. This version was designed as a tank destroyer by mounting the longer barrelled 75mm Type 90 anti-tank gun
Work commenced on the new version SPG in 1942, but again lack of raw materials meant that Ho-Ni II production was delayed a further year, with most units built spasmodically between 1944 and 1945. According to American sources, the Imperial Army received 62 units of the 105mm gunned SPG (other sources say it was 54) which were integrated into regular artillery units, each having a four vehicle battery. Several units were sent to operate with traditional artillery during the 1944-45 Philippines campaign as a component of the Japanese Fourteenth Area Army.
Whilst the American landings were unopposed, the Japanese inland defences were formidable, digging-in most of their tanks hull down creating static artillery positions. A few other Ho-Ni II SPGs were deployed in the final weeks of the Burma campaign, but the remainder were retained in defence of Honshu and Kyushu and thus never saw action. Following development of the Ho-Ni II came the Type 3 Ho-Ni III in late 1944. This SPG was fitted with the more-powerful 75mm Type 3 anti-tank gun in a fully-enclosed armoured hull superstructure, providing much needed protection for the gun-crew, but only 31 of these improved tank-destroyers were ever produced with no record found that they ever saw active service.
Left: The gun crew of the Type 1 Ho-Ni II were totally exposed to fire from the rear, as clearly illustrated in this photograph of the self-propelled gun being trialled during the winter of 1943
TYPE 1 Ho-Ni II SPG
- Crew: 5
- Weight: 14.60 tonnes
- Length: 5.55m
- Width: 2.29m
- Engine: Mitsubishi Type 97 SA 12200VD air-cooled V12 diesel engine
- Top speed on road: 38km/h
- Top speed off road: 29km/h
- Range: 200km
- Front armour: Hull 25mm, front shield 51mm
- Firepower: 105mm Type-91 howitzer
Left: Ho-Ni SPG prototype 1941: Japan’s first SPG used the 75mm Type-90 field gun on a Type 97 Chi-Ha chassis, but production was delayed until late 1942
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