Japanese 20mm Type 99 Cannon

Type 99 Model 1 cannon (flexible mount)
Top: Type 99 Model 1 Mark 3 cannon.
Bottom: Type 99 Model 2 Mark 3 cannon.
Photograph of Type 99 Model 1 cannon
U.S. Navy. Via Francillon (1979)

Photograph of Type 99 variants


Projectile weight    
4.5 ounces or 128 grams
Velocity 1970 feet per second or 600 meters per second (Model 1)
2490 feet per second or 759 meters per second (Model 2)
Range 2625 to 3280 feet
800 to 1000 meters
Gun weight
55 lbs or 25 kg (Model 1)
80 lbs or 36 kg (Model 2)
Rate of fire     
520 rounds per minute (Model 1)
490 rounds per minute (Model 2 Mark 3)
620 rounds per minute (Model 2 Mark 5)
Gun power
96 (Model 1)
120 (Model 2)

The Type 99 was the standard cannon on Japanese naval aircraft throughout the war, appearing in both fixed and flexible variants. It was based on the Oerlikon, for which the Japanese had negotiated a manufacturing license in 1936, but it was continually improved and refined. Early marks were known simply as E-shiki ("Oerlikon Type") guns, and it was not until 1941 and 1942 that the Model 1 and Model 2 were so designated. As with all Oerlikon variants, the Type 99 action was blowback with advanced primer ignition.

The Type 99 was not an outstanding weapon. Although its APIB action made the Type 99 one of the lightest aircraft cannon of the Second World War, suitable for the equally light Japanese Navy airframes, this came at the cost of a low muzzle velocity and rate of fire. The Type 99 was inferior to the Japanese Army's excellent Ho-5 cannon, which used a short recoil action, in every respect except overall weight. However, with the A6M "Zero" under design at the time that the Type 99 was adopted, weight was the preeminent consideration. It did not help that there was practically no cooperation between the Army and Navy on weapons systems and that the manufacturer of the Type 99, the Tomioka Weapons Works, had been set up by retired Navy officers.

The Model 1 was based on the Oerlikon FF and came in both fixed and flexible marks. Early models were fed from 60-round drums, but by 1942 this was replaced with a 100-round drum.  The Model 1 Mark 4 was belt-fed and had a slightly faster rate of fire than the other marks. All marks had rather low muzzle velocities, which initially made them unpopular with aircrew.

The Model 2 was based on the Oerlikon FFL and came into use as airframes became large and strong enough to accommodate the bigger, more powerful gun. However, the Model 2 did not completely close the performance gap with the Ho-5. All marks were fixed guns, though these were sometimes installed in mechanical turrets for use in flexible gun positions. As with the Model 1, early marks used 60- or 100-round drums, while the Model 2 Mark 4 and Model 2 Mark 5 were belt-fed. The Mark 5 introduced a number of innovations in the belt feed and bolt buffer to achieve a higher rate of fire, but it was not introduced until May 1945 and saw little service.

Photo Gallery

Photograph of Type 99 20mm cannon comparing model 1 and model 2 (both mark 3)
Photograph of Type 99 20mm cannon Mark 4
Photograph of Type 99 20mm cannon Model 2 Mark 1 and 4
U.S. Army
Photograph of Type 99 20mm cannon

Chinn (1951)


Chinn (1951; accessed 2013-9-12)

Francillon (1979)

Mikesh (2004)
Williams and Gustin (2003)

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