The US Navy's Iowa (four ships) class battleships carried a main armament of nine 16"/50 caliber guns in three triple turrets. The previous North Carolina (two ships) and South Dakota (four ships) classes carried a very similar main battery of nine 16"/45 caliber guns. These 10 ships, completed between 1941 and 1944, comprised the USN's "third generation" battleships and all saw service in WW II.

The designation 16"/50 means a 16" diameter shell and a barrel 50 calibers long. That would be 16x50=800 inches, or a barrel 66.66 feet long. The 16"/45 gun fired the same shells from a slightly shorter barrel 60 feet long.

The specifications for these hugely powerful naval rifles are interesting, although the details vary somewhat depending on the source. According to the American Rifleman magazine in 2017, each 16"/50 gun weighed around 390,000 pounds. Remember, American battleships carried nine of these guns!

The barrel had 96 rifling grooves (shades of Marlin's micro-groove type rifling, which is typical of cannons). The twist rate was one turn in 25 calibers, or 1:400". The maximum service pressure was 18.5 tons psi, or 37,000 pounds psi.

Shells of different weights were fired, weighing from approximately 1,900 to 2,700 pounds. The heaviest shell was the AP (armor piercing) projectile, which had a maximum range 42,345 yards from the 16"/50 gun, or 39,000 yards from the 16"/45 gun (about 22 miles).

According to Jane's Fighting Ships (circa WW II), the muzzle velocity (MV) was up to 2800 fps with a 2100 pound shell and muzzle energy was 98,406 ft. tons. The rate of fire was about two rounds per minute.

The 2700 pound "super heavy" 16" AP projectile, developed in 1939 for the third generation battleships, was supposed to be able to penetrate 16" thick steel armor plate at 28,000 yards. This gave the USN battleships' 16" guns penetration close to that of the Japanese 18.1" guns mounted on the contemporary Yamato class battleships, which fired a 3200 pound AP shell.

To put these numbers into perspective for the contemporary shooter and hunter, one the world's foremost big game hunting cartridges (and also a NATO military cartridge), the .308 Winchester, can also launch typical projectiles at a MV of 2800 from the 24" barrel of a hunting rifle. In this case the bullets have a diameter of .308" (less than 1/3 inch) and weigh 150 grains (0.34 ounce). The muzzle energy of this load is 2611 ft. lbs. (1.3 ft. tons).