Japanese Medium calibre anti-aircraft guns.

[JFC Fuller]

I have been looking for information on proposed Japanese WW2 medium calibre AA guns, mostly for naval applications. The only one I have come across is the 40mm Type 5 (copied from the bofors) however this never seems to have been made to work properly and was only ever built in single manually operated mountings. Navweaps insists that no other weapons were under development but this seems very odd. I would imagine that at least some effort was put towards solving the most obvious deficiencies of the 25mm? Does anybody have any more information?

Thank you in advance sealordlawrence.

 

[eltf177]

Japan did indeed build a 40mm cannon but this was a copy of the Vickers 2-pounder pom-pom, not the bofors. It existed in both single and twin mounts. The cruisers "Mikuma" and "Mogami" originally carried four single mounts as light cruisers, but when they were converted to heavy cruisers these were replaced with twin 25mm's and "Kumano" and "Suzuya" were completed with the 25mm's. There was a class of minelayers that carried a single 40mm forward but that was it. The twin mount was, as far as I know, only installed on land.

The IJN seemed content with the 25mm in single, twin and power-driven triple mounts. By the time they learned it was too short-ranged and lacked punch it was too late to do anything but put more on each ship and hope for the best. Personally I'm surprised they didn't get 37mm weapons from Germany or Italy for testing, or possibly the Soviet 45mm.

 

[Madurai]

There were some subchasers that used the twin 40 mount, too.

The only IJN AA project I recall that came to the hardware stage was the 4.7" rocket.

 

[tom!]

Hi.

There were 3 medium aa-guns adopted by the japanese armed forces:

IJN bought several Vickers 2pdr Pom-Poms from 1925 and used them on surface ships in single and twin-mounts. But it was outdated in 1935 and replaced by Type 96 2,5 cm automatic guns. A japanese licence or non-licence production is not mentioned. Some of these guns were later used for island defences.

IJA tested several european light and medium aa-guns in 1938/39 (at least a 20 mm Solothurn, a 20 mm Oerlikon, a 2 cm Flak 30 and a 3,7 cm Flak 18). The german 3,7 cm Flak 18 was found useful but too heavy. So there were trials to develop lighter lafettes for this gun. In 1941 one of three versions was officially adopted as "Type 1 Rheinmetall-Type 3,7 cm Automatic Gun" but serial production did not start.

In Malaya, Burma and the Dutch East Indies (Indonesia) 1941/42 IJA captured around 150 40 mm Bofors aa-guns but only few were operational. Due to the massive need in 1944 the decision was made to copy this gun and it was adopted as "Type 5 4 cm Automatic Gun". Serial production was about to be started at war´s end. Only few pre-series guns were finished.


It seems that there were no further trial to develop other medium aa-guns and I also wonder why.

It seems that until 1941 IJN and IJA were convinced the 20 mm and 25 mm guns were enough against low-flying aircraft and the 75 mm, 100 mm, 105 mm and 127 mm guns would be able to successfully fight high flying aircraft. From 1942 on there was a massive lack of ressources which only allowed the development of few new models, basically heavy guns (Type 4 75 mm, Type 3 120 mm, Type 5 127 mm and Type 5 150 mm).

Surely the strict IJA weight limitations for infantry weapons had also a heavy impact, at least on the army aa-guns. As light and medium aa-guns were considered infantry weapons they all should be light-weight for fast transport by few men or 1-2 horses in the field. To reach this the lafettes had to be light-weighted, too. This lead to structural problems due to the recoil forces which had to be compensated by the lafette. Often the only way to cope with this problem was to lower the recoil forces which also decreases the efficiency of the gun. There was a 57 mm at-gun/tank gun project which suffered so much from this problems that it had to be abandoned in 1942.

Yours

tom!

 

[Tzoli]

For some time I was trying to search for photos or even drawings of the 40mm Type 5 AA gun, but did not found any except this piece:
Which could be a captured gun but I'm not sure.

from:
http://togetter.com/li/794814

Does anybody ever found photos of this gun?
Apparently a single vessel got equipped with it:
http://www.navypedia.org/ships/japan/jap_ml_kamishima.htm
https://ja.wikipedia.org/wiki/%E7%A5%9E%E5%B3%B6%E5%9E%8B%E6%95%B7%E8%A8%AD%E8%89%87

And to be equipped:
http://www.navypedia.org/ships/japan/jap_aux_a.htm
http://www.navypedia.org/ships/japan/jap_aux_b1.htm

 

[Petrus]

For some time I was trying to search for photos or even drawings of the 40mm Type 5 AA gun, but did not found any except this piece:
Which could be a captured gun but I'm not sure.

from:
http://togetter.com/li/794814

Does anybody ever found photos of this gun?
Apparently a single vessel got equipped with it:
http://www.navypedia.org/ships/japan/jap_ml_kamishima.htm
https://ja.wikipedia.org/wiki/%E7%A5%9E%E5%B3%B6%E5%9E%8B%E6%95%B7%E8%A8%AD%E8%89%87

And to be equipped:
http://www.navypedia.org/ships/japan/jap_aux_a.htm
http://www.navypedia.org/ships/japan/jap_aux_b1.htm

I would say this is the Japanese-made gun rather than captured one. Its flash hider does not resemble that of a standard Bofors. The Japanese version used a Rheinmetall-pattern flash hider (similar to that for the 25mm gun), and for me what we may see here is the Rheinmetall device.

Piotr

 

[Petrus]

Here you've got an excerpt from a report of US Navy Technical Mission to Japan on the Type 5 40mm gun as well as a drawing of the 25mm gun Rheinmetal-type flash hider.

Another USNTMJ's report on muzzle brakes and flash hiders includes the following paragraph on the Type 5's flash hider:

The 40mm Bofors guns, which the Japanase had captured in Singapore, were equipped with the simple cone. Although the 40mm gun was never in service for the Japanese, sufficient test had been conducted to indicate that the simple cone type flash hider was unsatisfactory. Guided by the results obtained in case of the 25mm gun, the Navy next tried the Rheinmetal designed for the 40mm. The results were unsatisfactory, and the decision was made that a different type be designed. The end of the war precluded any work at all on the new design.

Piotr

 

[Tzoli]

I'm no naval gun expert, but what does this mean?
Is that the Japanese made Type 5 or the modified captured British Bofors?
(Note that I do not recognize what is the flash hider on it)

 

[Secundius]

Excuse me for pointing out that not all Bofors Guns produced by Bofors were Automatic. Both the Japanese Type 4 7.5cm/30-caliber (75x604mmR) and the Type 41 3rd year type 8.0cm/40-caliber (80x405mmR) were Breech-Loading AA Guns...