Japanese Air Force Cannons

The Imperial Japanese Navy and Army Air Forces took two different approaches when they decided to equip their aircraft with 20mm autocannons.

The Navy tested some Oerlikon 20mm autocannons, liked it and started local production of two Oerlikon-types, which they called Type 99-1 and Type 99-2. They’re really local copies of the Oerlikon FF and and the larger FFL. The Oerlikons (and therefore both Type 99’s) had a rather low rate of fire. Type 99-1 had low muzzle velocity in addition.

The A6M Zero was equipped with wing-mounted Type 99-1, muzzles flush with the leading edges. Later versions of the fighter were equipped with the longer Type 99-2 with muzzles portruding from the wing edges. Zero pilots generally didn’t like firing the earlier cannons, they were slow-firing and only good at very close range on slow-moving targets. Pilots relied more on their cowl machine guns. Instead of blasting their foes with a few cannon shots, pilots like Saburo Sakai would hang on their target’s tail and pour their two machine guns on it. And sometimes the target would just keep on flying.

The Army got in a bit later and with an approach I found very interesting. They started out with the Ho-103 12.7mm machine gun, a local version of the American Browning 1921 .50 caliber that Americans nickname the “Ma Deuce”, modified to use shorter cartridges to improve rate of fire.

Then they simply scaled up all the parts, loaded it with explosive shells, and got a very decent autocannon indeed, the Ho-5 , with faster muzzle velocity and higher rate of fire than the Navy’s Oerlikon derivatives. Some have called it the best autocannon of WW2, and even some Americans wonder why their own forces didn’t simply upsize their beloved “Ma Deuce” to fire shells. The Ho-5 was only slightly heavier than the 50 cal Browning, and packed a bigger punch per weight.

(The Americans really did consider cannon-arming their single-engine fighters, as can be seen in the P-39 Airacobra. They tried producing Hispano-Suiza cannons but their contractors botched it.)

The Ho-5 went to equip the Ki-44 Shoki, Ki-84 Hayate and Ki-45 Toryu, and generally, the Army pilots fired their cannon more often than their Navy counterparts.

If the Navy’s aircraft cannons were so inferior, why didn’t they switch to Army gear? Well, there was a fierce rivalry between the two arms. They would even design aircraft that shared no common spare parts, and use mutually incompatible ammunition.

And then there was the cartel of retired-Admirals-turned-contractors supplying the Type-99’s, they were really tight with the Navy and elbowed out any competition, let alone allow Army equipment into the Navy system.

The Navy worked around the Type 99-2’s low rate of fire by putting more of them on their planes when possible: the Kawanishi N1K Shiden and Shiden Kai carried four of them, as did the Mitsubishi J2M Raiden. Late-war A6M5 Zeros complemented their two wing cannons with two wing-mounted heavy machine guns. They would have mounted four cannons in the Zero if only there had been room, and the weight of doubled armament compromised the Zero’s chief advantage: agility.

Late war Japanese Army fighters made do with two Ho-5. It was enough.

Zeros equipped with Ho-5 would have remained useful late-war, retaining its agility while delivering a good punch from longer range. When your enemies are faster than you, you need to be able to hit them even as they pull further away and make the kill before they escape. Having a good firing rate helps to hit the target as well.

It was a strange compliment to the Browning Ma Deuce, that an upsized version of it firing shells became a favourite weapon of the Imperial Japanese Army Air Force.

Some data:

Army Ho-5:

Caliber: 20 mm (0.8 in)
Ammunition: 20 x 94 (84.5 g)
Weight: 35 kg (77 lb)
Rate of fire: 450-600 rounds/min (some sources put it as high as 950 )
Muzzle velocity: 750 m/s (2,460 ft/s)

Navy Type 99:

799px-Navy Type 99-1 & 99-2


Type 99-1:
Caliber: 20 mm
Ammunition: 20x72RB
Length: 133 cm (53 in)
Weight: 23 kg (51 lb)
Rate of fire: 520 rounds/min
Muzzle velocity: 600 m/s (1970 ft/s)

Type 99-2:
Caliber: 20 mm
Ammunition: 20x101RB
Length: 189 cm (74 in)
Weight: 34 kg (75 lb)
Rate of fire: 480 rounds/min
Muzzle velocity: 750 m/s (2460 ft/s)


2 thoughts on “Japanese Air Force Cannons

  1. The IJA Ho-5 was downgraded in M/V late in the war so range fell from 900m to 600m. These cannons still had world-class 850 average rate of fire. Thus they remained OK for wing-cannons. In the cowl, the Ho-5 was penalyzed over half it’s rate, to fire through the prop and now it was short range too. However in the wings, convergence was under 600m anyway, so the degraded M/V was less of a factor. This was to save rare metals mostly.

    About the same time the faster IJN Typ 99-II Mk 5 began production. It had up to 750 r/m rate as well as retaining M/V. Range was 914m.

    there was an alternative IJN 20mm cannon that wasn’t produced, but it was not as good as the Type 99-II Mk 5 in any case.

    The D4Y2-S Judy night fighter could’ve possibly had a motor-cannon since it had an inline engine.
    An IJN 30mm Type 5 could be used. It had the heaviest 30mm shell in the war at 345g and still 900m firing range. RoF was 350 to 450 r/m. It was not Oerlikon or Browning-based. It was a Japanese original so it may have been OK for synchronizing without prohibitive penalty. If so, it could be on the cowl of radial powered fighters.
    As it was, the D4Y2-S Judy used a slanted dorsal 20mm Type 99 cannon like the A6M5d-S Zero night fighter did. These should’ve tried 30mm cannons to be more effective against B-29s. More hp would’ve helped in this upgrade. Alternatively, in the case of the Zero, all three of it’s 20mm cannons could’ve been concentrated together on a slant to clear the prop arc.
    This means dogfighting marksmanship would be easier too. Pulling lead on a targeted fighter without him ducking under the nose to hide so easily, especially if it’s a bigger Ha-112 or Ha-211 (MK9) radial engine.

    The Ki 61 had similar larger cannon choices for a motor-cannon.

  2. The IJA 20mm Ho-3 was the opposite of the Ho-5.
    It had the heaviest 20mm shells of WW2, the Ho-5 had the lightest.
    It had the slowest rate of fire at 400 r/m, the Ho-5 had the fastest at 850.
    It was hardly used by fighters, the Ho-5 became the IJAAF standard 20mm.
    It had the best M/V, the downloaded Ho-5 had just OK M/V.
    The Ki 45 used both.
    Rather than use the Ho-3, the early Ki 61 installed imported Mausers before the Ho-5 was ready. I imagine this was because of the very slow fire rate of the Ho-3 for dogfighting. It made the Hispano look fast. This would have been offset by a quartet of them, however. That would be heavy though.

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