The 16"/50 (40.6 cm) caliber gun Mark 7 was the main armament of the Iowa-class battleships. This was possibly the best battleship gun ever put into service. Originally intended to fire the relatively light 2240 pound (1016 kg) AP Mark 5 projectile, the shell handling system for these guns was redesigned to use the "super-heavy" 2700 pound (1224.7 kg) AP Mark 8 before any of the USS Iowa class (BB-61) battleships were laid down.
These guns were 50 calibers long—or 50 times their 16-inch (406mm) bore diameter which makes the barrels 66.6 feet (20 m) long, from breechface to muzzle. Each gun weighed about 239,000 pounds (108,000 kg) without the breech, or 267,900 pounds (121,517 kg) with the breech. They fired projectiles weighing from 1900 to 2700 pounds (850–1200 kg) at a maximum speed of 2,690 feet per second (820 meters per second) with a range of up to 24 miles (39 km).
At maximum range the projectile spent almost 1½ minutes in flight. Each turret required a crew of 79 men to operate. As modernized in the 1980s, each turret carried a DR-810 radar that measured the muzzle velocity of each gun, which made it easier to predict the velocity of succeeding shots. Together with the Mark 160 FCS and better propellant consistency, these improvements made these weapons into the most accurate battleship-caliber guns ever made.
Description [partially] lifted from NavWeaps.com.
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Tier: 9-A, 7-C with Mark 23
Name: 16”/50 caliber Mark 7
Origin: Real World
Classification: Battleship Main Gun
Attack Potency: Small Building level+ with conventional shells (260–580 megajoules), Town level with Nuclear Mark 23 (15–20 kilotons); 1–2 rounds per minute rate of fire
Speed: Supersonic (550–820 meters per second), Supersonic+ (up to 1390 meters per second) with Long Range Bombardment Ammunition (post-late 1960s only)
Durability: At least Small Building level, at most City Block level with biggest turret mount in terms of total destruction (comprised of up to 1,856,920 kilograms of steel, which has a fragmentation energy of 49.2 gigajoules)
Stamina: Barrel life of 290-350 rounds
Range: Up to over 38 kilometers (AA ceiling of 7 kilometers), at least 67 kilometers with Long Range Bombardment Ammunition (post-late 1960s only)
Weaknesses: Manually loaded, requires about 94 men to operate one turret
Note: Similar naval guns of about the same bore (400-410mm) and period generally have performance equivalent to this one.