Machine guns on the Nakajima Ki-43 Hayabusa

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About those Ki-43 machineguns

During the great duel for Lowing in April 1942, the Japanese army's 64th Sentai was equipped with a later-model version of its retractable-gear fighter, the Nakajima Ki-43 Hayabusa (called "Oscar" by Allied pilots and by US historians who are reluctant to use Japanese terms).

Pre-production models of the Hayabusa had two fixed machineguns in the nose, synchronized to fire through the propeller arc, one 7.7 mm and the other 12.7 mm (respectively equivalent to British caliber 0.303 and U.S. caliber 0.50). By the time they went into combat, however, those planes had been relaced by the up-gunned Ki-43-I, whose usual armament was two large-caliber machineguns. In their postwar memoirs, Japanese pilots reported that the results were disappointing: the large-caliber gun fired so slowly that on many of their fighters, the armorers replaced the port weapon with the older 7.7 mm gun, thus restoring the armament mix of the earlier plane.

When I noted this action on the moderated World War II newsgroup, British weapons scholar Tony Williams challenged it, pointing out that the 12.7 mm gun fired at about the same rate as the smaller gun. So here we had a classical example of a historian contradicting the memory of the man on the scene. My inclination in this case was to go with the Japanese pilot's recollection, and it seems I was right, because along came Robert Mikesh with a book published by Schiffer, Japanese Aircraft Equipment, 1940-1945. Bob Mikesh was one of my mentors at the National Air & Space Museum when I was a Verville fellow there, translating those same pilot memoirs and other books.

Type 89 7.7 mm gun

Shown above is the army's Type 89 machinegun, so-named because it went into service in the Imperial Year 2589 (1929 by the western calendar). Derived from the .303-caliber British Vickers gun, it fired a 7.7x58 mm semi-rim cartridge with a muzzle velocity of 820 meters/second and a rate of fire of 900 rounds per minute. Significantly, Mikesh notes: "The Type 89 synchronized well." In the photo above, the cable extending forward connects the gun to the synchronizing gear in the propeller transmission; the cable attached to the breech was to cock and charge the weapon. The gun's length was 1.035 meters or a bit less than 41 inches; a seven-bullet section of linked ammunition is shown in front of the weapon.

Type 89 stinger This was the gun that equipped the Nakajima Ki-27 "Nate" that the AVG regularly encountered over Burma and China, and one of which was also on the early model Ki-43s. The same gun armed the Ki-30 "Ann" light bomber. A flexible version was the standard armament on the medium and heavy bombers met by the AVG. Shown at left is the flexible Te-1 gun used as the "stinger" in the tail of a Ki-21 "Sally" heavy bomber. In this case, the gun was aimed remotely by the greenhouse gunner, using cables that tracked his swivel-mounted weapon; he could fire it by pulling a lanyard. His own weapon was a drum-fed two-barrel version, the Type 89 (special) that boasted an interesting vane-type front sight, which was supposed to deflect in the slipstream to account for the lead required in deflection shooting.

Type 1 12.7 mm gun

In the Imperial Year 2601 (1941), the Japanese army adopted its Type 1 "13 mm" machinegun—or machine cannon, as the Japanese reckoned anything larger than 11 mm. The gun was in fact chambered for a 12.7x81 mm semi-rim cartridge adapted from an Italian round.

Rather than adopt the Italian gun, however, the Japanese borrowed the design of the US Model 1921 Browning 13 mm or 0.50 caliber aircraft machinegun. (Marrying the American weapon to the Italian cartridge, Mikesh notes, was "no mean feat.") The gun was scaled down in size, and a muzzle booster was added to enable the smaller cartridge to operate the gun. You can see the muzzle booster at left above. Note the large size of the linked bullets as compared to those with the Type 89 gun, even though the Type 1 is considerably longer at 1.267 meters (about 50 inches).

"The result was very successful," Mikesh writes, "but, like all Brownings, the gun did not synchronize well, losing much of its rate of fire." Its promised rate of fire, 900 rounds per minute, dropped to as low as 400 rpm in practice.

So Lieutenant Hinoki and Tony Williams have been reconciled: the Type 1 was a perfectly respectable gun that, when installed in the Nakajima Hayabusa, had its rate of fire reduced so much that it was the despair of the men who flew it.

For more on this, see Joe Baugher's Hayabusa files and Richard Dunn's monograph on Nakajima Ki-43 Hayabusa armament on this site. (Mr Dunn sides with Tony Williams and against the pilots who were there.)

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