Robert Mikesh has created another of those remarkable books from
Schiffer, and unlike most Schiffer books it is farily free from
typographical and grammatical errors.
Japanese Aircraft Equipment, 1940-1945
In the chapter on machine guns, he notes that the Japanese called
anything over 11 mm a machine cannon. So the standard heavy machine
gun of 12.7 or 13 mm were, by their reckoning, cannon.
Indeed, the Navy Type 3 was 13.2mm. There was even a Navy experimental
gun (14-shi) with a 20 mm Oerlikon necked down to 14 mm. I suppose
that would rate as a cannon by both the Japanese and the western
Mikesh's book, by the way, resolves a debate about the large-caliber
gun in the early Ki-43 Hayabusa or Oscar fighter. Japanese pilot
accounts relate that it was so slow-firing that in some planes the
weapons were field-refitted to 7.9 mm. Yet western experts say the gun
was suitably quick-firing.
Mikesh notes that the Army Type 89 7.7mm fixed machine gun was a
Vickers type that "synchronized well." The Army Type 1 12.7mm (also
called 13 mm and Ho-103) wedded an Italian 12.7 mm cartridge to a U.S.
Model 1921 Browning mg ("no mean feat", says Mikesh). "Like all
Brownings, the gun did not synchronize well, losing much of its rate
Whereas the 7.7mm fired 900 rounds per minute, the 12.7mm when
synchronized to fire through the propeller had a rate of fire as low
as 400 rpm even though its theoretical rpm in wing mount was also 900.
This would explain the vastly different accounts given by experts in
an office and pilots in the field, and why a pilot might prefer the
smaller caliber gun.
all the best -- Dan Ford
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