The 5"/38 (12.7 cm) caliber gun Mark 12 was a US naval gun. It was unquestionably the finest dual purpose gun of World War II. Originally designed to arm new destroyers being built in the 1930s, the 5"/38 (12.7 cm) wound up being used on nearly every major US warship built between 1934 and 1945 and was still being used on new construction as late as the 1960s.
It was also used on many auxiliaries, merchant vessels and smaller warships as well as on US Coast Guard vessels. This standardization, unique in any navy, greatly helped the logistical supply situation of the Pacific War. United States naval gun terminology indicates the gun fired a projectile 5 inches (127mm) in diameter, and the barrel was 38 calibers long, making the 5"/38 dual purpose midway in barrel length between the 5"/51 surface-to-surface and the 5"/25 anti-aircraft guns. The increased barrel length provided greatly improved performance in both anti-aircraft and anti-surface roles compared to the 5"/25 gun.
Description partially lifted from NavWeaps.com.
Powers and Stats
Name: 5”/38 caliber Mark 12
Origin: Real World
Classification: Destroyer/Light Cruiser Main Gun, Heavy Cruiser/Battleship Secondary Gun
Attack Potency: Small Building level (6.6–29 megajoules); 10–15 rounds per minute rate of fire
Speed: Transonic to Supersonic (366–792 meters per second)
Durability: At most Building level with biggest turret mount in terms of total destruction (Comprised of up to 79,210 kilograms of steel with a fragmentation energy of 2.1 gigajoules)
Stamina: Barrel life of 4600 rounds
Range: Up to over 16 kilometers (AA ceiling of just under 12 kilometers)
Weaknesses: Manually loaded, requires about 27 men to operate a twin gun turret
Note: Similar naval guns of about the same bore (120-130mm) and period generally have performance equivalent to this one.