Armament of The Iowa Class Battleship - Main Battery - Turrets

Turrets

The primary armament of an Iowa-class battleship consisted of nine breech-loading 16 inch (406 mm)/50-caliber Mark 7 naval guns, which were housed in three 3-gun turrets: two forward and one aft in a configuration known as "2-A-1". The guns were 66 feet (20 m) long (50 times their 16-inch (410 mm) bore, or 50 calibers, from breechface to muzzle). About 43 feet (13 m) protruded from the gun house. Each gun weighed about 239,000 pounds (108 000 kg) without the breech, or 267,900 pounds with the breech. They fired projectiles weighing from 1,900 to 2,700 pounds (860 to 1,200 kg) at a muzzle velocity of 2,690 ft/s (820 m/s) to a maximum range of 42,345 yards (38,720 m) (24.06 mi) using an armor-piercing shell.

Each gun rested within an armored turret, but only the top of the turret protruded above the main deck. The turret extended either four decks (Turrets 1 and 3) or five decks (Turret 2) down. The lower spaces contained the equipment required to rotate the turret and to elevate the guns attached to each turret. At the bottom of the turret were rooms which were used for handling the projectiles and storing the powder bags used to fire them. All of the compartments within the turrets were separated by flameproof bulkheads to prevent any flame or lethal gas from spreading throughout the turret. Each turret required a crew of 77—94 men to operate. The turrets were not actually attached to the ship, but sat on rollers, which meant that if the ship were to capsize the turrets would fall out. Each turret cost US $1.4 million, but this number did not include the cost of the guns themselves.

The turrets were "three-gun," not "triple," because each barrel could be elevated and fired independently. The ship could fire any combination of its guns, including a broadside of all nine. Contrary to myth, the ships do not move noticeably sideways when a broadside was fired.

The guns could be elevated from −5° to +45°, moving at up to 12° per second. The turrets could be rotated about 300° at a rate of about four degrees per second and can even be fired back beyond the beam, which is sometimes called "over the shoulder." The guns were never fired horizontally forward (in the 1980s refit, a satellite up-link antenna was mounted at the bow). To distinguish between the rounds fired from different battleships the Iowa class used dye bags which allowed artillery observers to determine which rounds had been fired by which ship. Iowa, New Jersey, Missouri, and Wisconsin were assigned the colors Orange, Blue, Red and Green, respectively.

Within each turret a red stripe on the wall of the turret, inches from the railing, marked the boundary of the gun's recoil, warning the crew to keep back.

When brought into service during World War II the guns had a barrel life of roughly 290 rounds, limited in large part by the Nitrated-Cellulose (NC) propellant. After World War II the Navy switched to smokeless Powder Diphenylamine (SPD), a cooler-burning propellant, which increased the barrel life from 290 to about 350 rounds. This was increased further by the introduction of a titanium dioxide and wax compound known as "Swedish Additive" on New Jersey for her tour in Vietnam, and later used on all four Iowas when they were reactivated in the 1980s. These measures were further augmented by the addition of polyurethane jackets, which were placed over the powder bags to reduce gaseous erosion during the firing of the guns. These measures greatly prolonged barrel life, and ultimately resulted in a shift from measuring barrel life in Equivalent Service Rounds (ESR) to measuring barrel life in Fatigue Equivalent Rounds (FER).

After the guns were fired, each rifle barrel had to be cleaned. Unlike small caliber guns which can be field-stripped, the guns aboard an Iowa-class battleship could not be disassembled, so the gunners mates assigned the job of cleaning the rifles required a full day or more to ensure that the barrels were correctly and adequately cleaned. To clean the rifles, a bore brush was lifted by two sailors and inserted into the gun barrel, where it was pulled through the rifle with the same equipment used to load the shells. Within the turret, crewmen checked to ensure that the breech fittings were properly cleaned and lubricated, while sailors outside the turret scraped off soot, and painted over flash burns left from the explosive expulsion of the 16-inch shells from the gun barrels.