Developed in the 1930s, the Type 99 was the go-to 20mm autocannon for Japanese military aircraft, serving as the wing guns, flexible mounts and powered turret mounts on a number of Japanese fighters and bombers, including the A6M "Zero" carrier-launched fighter of Pearl Harbor fame. Like many combatants on both sides of the Axis/Allies divide, the Japanese design directly follows the pattern established by the Oerlikon autocannon, using an advanced primer ignition (API) mechanism to reduce the amount of breech locking needed to fire the potent 20mm cannon round while also permitting a high rate of fire. This Mark 1 cannon is configured for the flexible defensive mount role, with the mounting point for the (not included) ammo drum on the underside to keep it out of the gunner's line of sight, and an ejector port shroud to direct the spent casings to the shooter's right. A heat shield assembly protects the back half of the barrel, the recoil spring, and the bolt extensions, with a ratcheting hand-cracked charging mechanism on the right side. The left side of the trigger housing bears the Japanese model nomenclature, with dual pistol grips and a slot on the back for installing a (not included) buttpad. Sights absent.

Very fine, with 80% of the original black finish, showing mild wear and spotting overall, some dents on the heat shield, and mild handling marks overall. Some rust is present on the interior. The mechanism appears to be in fine order. NOTE: This weapon is a National Firearms Act (NFA), fully transferable Class 3, which is registered with the Bureau of Alcohol, Tobacco, Firearms and Explosives, (BATFE) that is classified as a "Curios or Relic" as defined in 27 CFR, 478.11. These weapons are still subject to the provisions of 18 U.S.C. Chapter 44 and 27 CFR part 479.