12.7 cm/50 Type 3 naval gun

The 12.7 cm/50 Type 3 naval gun was a medium calibre naval gun of the Imperial Japanese Navy used during World War II. It was the standard weapon for Japanese destroyers between 1928 and 1940. It has been credited as a true dual-purpose gun, but this was more a nominal capability than real as its bag propellant and need for hand ramming required the gun to be loaded at angles between 5–10° which dropped its rate of fire to a relatively slow 5–10 rounds per minute and its training speed of only 6° per second meant that it had a great deal of difficulty engaging enemy aircraft with any chance of success. After the end of World War II the gun remained in service on the two Japanese destroyers ceded to the Soviet Union and the Republic of China as war reparations, the last of which was scrapped in 1970 after running aground in a typhoon.

Description
The 50 caliber 12.7 cm Type 3 gun was "of built-up construction, originally with three and later two layers with the usual breech ring and breech bush." It used a Welin interrupted screw breech. The shell was fuzed manually on the loading tray before being rammed by hand and could only be loaded at elevations between 5° and 10°. All mounts used pusher type shell hoists, but the powder bags were passed by hand.

Mountings
These guns were first used in the twin gun Model A turret on the revolutionary Fubuki-class destroyers. These were the first weatherproof, splinterproof and gas-proof enclosed gun turrets ever mounted on a destroyer. Guns in twin mounts were in individual cradles and could elevate separately. All twin gun mounts weighed approximately 32 t. All mounts could traverse at 6° per second and could elevate at a rate between 6° and 12° per second although speeds up to 27° per second have been reported.

The twin gun Model A mount was fitted with a 9 - 12 mm thick gun shield. Its guns could depress −5° and elevate to +40°. These mounts were deployed on the first ten Fubuki-class destroyers. The twin gun Model B mount had its elevation increased to 75° and was fitted in the rest of the Fubuki-class as well as the Akatsuki-class destroyers. In order to save weight its gun shield was reduced to 3.2 mm in thickness, but this proved too thin to withstand heavy seas and was later reinforced. The first four Hatsuharu-classs used the Model B mod 2 mount although how it differed from the earlier Model B mount is unknown. The last two of the Hatsuharu-class, the Shiratsuyu-class, the Asashio-class, and the Kagerō-class destroyers used the Model C which reduced its maximum elevation to 55°, but could depress to −7° and was supposedly lighter than earlier models The Model D used by the Yūgumo-class and the Shimakaze destroyers retained the depression limit of the Model C, but elevation returned to the 75° of the Model B.

The Type A single mount could depress −7° and elevate to +75°, but the Type B reduced the maximum elevation to 55°. Both mounts weighed approximately 18.5 t. The Type A was fitted on the Hatsuharu-class and the Type B on the Shiratsuyu-class destroyers.

Ammunition
The gun normally fired a 23 kg high-explosive shell, an illumination shell or an incendiary shrapnel round (sankaidan) intended for anti-aircraft use. All of these shells weighed 23 kg and used 7.7 kg of 30 DC propellant. After 1943, a flat-nosed anti-submarine shell also became available. This had a minimum range of 800 m and a maximum range of 4300 m. An new, heavier, but more streamlined, high-explosive projectile with a range of 23025 m was under development when the war ended.