25mm-60 caliber gun
Based on a French Hotchkiss design, the Imperial Japanese Navy's primary light to medium antiaircraft gun gave little protection to even Yamato-class battleships. Inferior even for a gun in the 20mm range, which, by 1944, was being deemphasized by other countries in favor of longer-ranged, more lethal 40mm and 5" guns, the 25-60 suffered from a number of engineering flaws. 
While the gun had a reasonable rate of fire when it was firing, it was loaded with 15-round fixed magazines that did not allow continuous reloading. Its aiming and training rate was slow and it only had visual and manual fire control, made worse by its excessive vibration.
The Japanese might say a battleship had 120 antiaircraft guns, but if most were of this type, they were virtually useless. Due to the short range of the 25mm, they only could be used for local ship defense, not area defense. IJN Musashi primarily protected with these weapons, was sunk, during the Battle of Leyte Gulf, with the loss of only 18 U.S. aircraft.
- Japanese Naval Ordnance: 25mm/60 caliber, Combined Fleet.com