The s are the most heavily armed warships the United States Navy has ever put to sea, due to the continual development of their onboard weaponry. The first Iowa-class ship was laid down in June 1940; in their World War II configuration, each of the Iowa-class battleships had a main battery of guns that could hit targets nearly 20 statute miles (32 km) away with a variety of artillery shells designed for anti-ship or bombardment work. The secondary battery of guns could hit targets nearly 9 statute miles (14 km) away with solid projectiles or proximity fuzed shells, and was effective in an anti-aircraft role as well. Each of the four battleships carried a wide array of 20 mm and 40 mm anti-aircraft guns for defense against enemy aircraft.
When reactivated and modernized in the 1980s, each battleship retained the original battery of nine guns, but the secondary battery on each battleship was reduced from ten twin-gun mounts and twenty guns to six twin-gun mounts with 12 guns to allow for the installation of two platforms for the Tomahawk missiles. Each battleship also received four Harpoon missile magazines, Phalanx anti-aircraft/anti-missile systems, and electronic warfare suites.
Main battery
Turrets
The primary armament of an Iowa-class battleship consisted of nine breech-loading 16 inch (406 mm)/50-caliber Mark 7 naval guns,Originally the armament was to be nine 16"/50 (406 mm) Mark 2 Naval Guns intended for the canceled s; however, a miscommunication between the design bureaus resulted in the Iowa class being equipped with the Mark 7 Naval Guns instead. DiGiulian, Tony. United States of America 16"/50 (40.6 cm) Mark 7. navweaps.com Retrieved on 2007-03-25. which were housed in three 3-gun turrets: two forward and one aft in a configuration known as "2-A-1". The guns were long - 50 times their 16-inch(406mm) bore, or 50 calibers, from breechface to muzzle. About protruded from the gun house. Each gun weighed about without the breech, or with the breech.For comparison, the Space Shuttle Orbiter, when fully loaded, weighs about , so each battleship gun is roughly the weight of a space shuttle orbiter. Schorr, Ben M. USS Missouri Frequently Asked Questions. factplace.com Retrieved on 2007-03-25. They fired armor-piercing projectiles at a muzzle velocity of , or high-capacity projectiles at , up to .
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.
Although frequently referred to as "triple gun" turrets, they were, in fact, classified as "three gun" turrets, due to the ability to elevate and fire each gun in the turret independently. This is as opposed to true "triple gun" turrets, in which all three guns must be operated as one. The ships could fire any combination of their guns, including a broadside of all nine.
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 could 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.
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 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 barrel had to be cleaned; the gunners mates assigned the job of cleaning them required a full day or more to ensure that the barrels were correctly and adequately cleaned.
Fire control The early main battery fire control consisted of the Fire Control Tower, two Mark 38 Gun Fire Control Systems (GFCS), and fire control equipment located in two of the three turrets. 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, the improvements created the most accurate battleship-caliber guns ever made.
Mark 38 gun fire control system The major components of the Mk 38 Gun Fire Control System (GFCS) were the Director, Plotting Room, and interconnecting data transmission equipment. Two systems, forward and aft, were each complete and independent, though they could be cross-connected. Their plotting rooms were isolated to protect against battle damage propagating from one to the other.
Director
The forward Mk 38 Director (pictured) was situated on top of the fire control tower. The director was equipped with Mark 45 Rangefinder optical sights (the long thin boxes protruding from each side), and a Mark 13 Fire Control Radar antenna (the rectangular shaped box on top). The purpose of the Director was to track the target's present bearing and range. This could be done electronically with the radar (the preferred method), or optically by the men inside using the sights and Rangefinder. The present position of the target was called the Line-Of-Sight (LOS), and it was continuously sent down to the Mk 8 Rangekeeper in the plotting room by Synchro transmitters. When not using the radar's display to determine Spots, the director was the optical spotting station.
Plotting room
The forward main battery plotting room was located below the waterline and inside the armored belt. It housed the forward system's Mark 8 Rangekeeper, Mark 41 Stable Vertical, Mk13 FC Radar controls and displays, Parallax Correctors, Fire Control Switchboard, battle telephone switchboard, battery status indicators, assistant Gunnery Officers, and Fire Control Technicians (FTs).
The Mk 8 Rangekeeper was an electromechanical analog computer whose function was to continuously calculate the gun's bearing and elevation, Line-Of-Fire (LOF), to hit a future position of the target. It did this by automatically receiving information from the director (LOS), the FC Radar (range), the ship's gyrocompass (true ship's course), the ship's Pitometer log (ship's speed), the Stable Vertical (ship's roll and pitch), and the ship's anemometer (relative wind speed and direction). Also, before the surface action started, the FTs made manual inputs for the average initial velocity of the projectiles fired out of the battery's gun barrels, and air density. With all this information, the Rangekeeper calculated the relative motion between "OWN SHIP" and "TARGET". It then could calculate an offset angle and change of range between the target's present position (LOS) and future position at the end of the projectile's time of flight. To this bearing and range offset, it added corrections for gravity, wind, Magnus effect of the spinning projectile, earth's curvature, and coriolis effect. The result was the turret's bearing and elevation orders (LOF). During the surface action, range and deflection Spots and target altitude (not zero during Gun Fire Support) were manually entered.
The Mk 41 Stable Vertical (also called Gun Director) was a vertical seeking gyroscope. Its function was to establish and maintain a stable earth vertical with its associated horizontal plane. With the horizontal plane established, the Mk 41 continuously measured the angles between the deck and the horizontal plane. These deck angles were continuously transmitted to the Rangekeeper so that it could keep the guns correctly elevated as the ship rolled and pitched. Mounted waist high on its side were the battery's firing keys. (see picture) The left key was the Salvo Signal Key, and it sounded the Salvo Buzzer in each of the turrets to warn the gun crews that the guns were about to fire. The center key (with bumps on its handle for tactile identification) was the Automatic Firing Key. When this key was held closed, the Mk 41 was enabled to automatically fire the guns whenever the ship's deck was parallel the horizontal plane. Also, if the sea state was such that the turrets' elevation power drives could not keep up with the ship's motion, the guns could be held at a fixed elevation, and the MK 41 could again automatically fire the guns as described. The right key was the Hand Firing Key. It bypassed the Mk 41, and fired the guns directly.
The Mk 13 FC Radar supplied present target range, and it showed the fall of shot around the target so the Gunnery Officer could correct the system's aim with range and deflection spots put into the Rangekeeper. It could also automatically track the target by controlling the director's bearing power drive. Because of radar, Fire Control systems were theoretically to track and fire at targets at a greater range and with increased accuracy during the day, night, or inclement weather. This capability gave the United States Navy a major advantage in World War II, as the Japanese did not develop radar or automated fire control to the level of the US Navy and were at a significant disadvantage.
The Parallax Correctors were needed because the turrets were located hundreds of feet from the director. There was one for each turret, and each had the turret/director distance manually set in. They automatically received Relative Target Bearing (bearing from own ship's bow), and Target Range. They corrected the bearing order for each turret so that all rounds fired in a salvo converged on the same point.
The Fire Control Switchboard configured the battery. With it, the Gunnery Officer could mix and match the three turrets to the two GFCSs. He could have the turrets all controlled by the forward system, all controlled by the aft system, or split the battery to shoot at two targets.
The assistant Gunnery Officers and Fire Control Technicians operated the equipment, talked to the turrets and ship's command by sound-powered telephone, and watched the Rangekeeper's dials and system status indicators for problems. If a problem arose, they could correct the problem, or reconfigure the system to mitigate its effect.
Turret fire control systems Turrets 2 and 3 had optical rangefinders and ballistics computers. (The rangefinders are the boxes on the turret's rear corners). If in a surface action the GFCSs were damaged, the Turret Officer could turn the Auto-Local rotary switch to Local and continue the action using the turret's fire control equipment.
Ammunition