Japanese 20mm Cannon Type 99
Technical Information

Background
Adopted in 1939, the Japanese 20mm cannon Type 99 Model 1 (short barrel) and Type 99 Model 2 (long barrel) were license built versions of the Oerlikon FF and Oerlikon FFL 20mm cannon.

Type 99 Model 1 (Type 99-1)
First used as the secondary armament of the A6M2 Zero with a 60 round drum magazine. The same weapon with a pistol grip was used in crew operated flexible mounts in bombers including the G3M Nell and G4M Betty bombers also in seaplanes including the E13 Jake and flying boats including the H6K Mavis and H8K Emily. Smaller saddle magazines were used holding 45, 30 or 15 rounds. This cannon was slow to reload and had a relatively slow muzzle velocity and rate of fire.

Type 99 Model 2 (Type 99-2)
Long barrel version with a higher rate of fire and muzzle velocity of roughly 670-750 rounds per minute, stronger buffer springs with a 100 round drum magazine. This cannon was installed later model A6M3 Zero and later models, plus other Navy fighters including the N1K Rex and N1K2 George.

Type 99 Model 3 (Type 99-3)
Fixed mount model that could mount a large 100 round ammunition drum.

Type 99 Model 4 (Type 99-4)
Fixed mount belt fed mechanism developed by Kawamura.

Type 99 Model 5 (Type 99-5)
Developed in May 1945, this cannon had stronger buffer springs with a rate of fire between 670–750 rounds per minute (rpm). It is unknown if this model was used in combat.

Technical Details (Type 99 Model 1)
Magazine  (fixed mount) 60 round drum or 100 round drum
Types  Ball, A.P., A.P./I., T., H.E., H.E./T., H.E./I.
Rate of fire  520 rounds per minute (rpm)
Muzzle velocity  600 m/s / 1,970 f/s