Armament of the Iowa-class battleship

USS Wisconsin, photographed at sea in her 1980s configuration.

The armament of the Iowa-class battleships has undergone a massive evolution since the first Iowa-class ship was laid down in June of 1940; The Iowas remain among the most heavily armed ships the United States ever put to sea. The main battery of 16 inch guns could hit targets nearly 24 miles (39 km) away with a variety of artillery shells, from standard armor piercing rounds to tactical nuclear charges called "Katies" (from "kt" for kiloton). The secondary battery of 5 in guns could hit targets nearly 9 miles away with solid projectiles or proximity fused shells, and were equally adept in an anti-aircraft role and for damaging smaller ships. When commissioned these battleships carried a fearsome array of 20 mm and 40 mm anti-aircraft guns, which were gradually replaced with Tomahawk and Harpoon missiles, Phalanx anti-aircraft/anti-missile gatling gun systems, and electronic warfare suits. No other battleship in history has had so many weapons at its disposal for use against an opponent.

Main battery

USS Iowa fires a full broadside of nine 16 inch (406 mm) / 50-caliber and six 5 inch (127 mm) / 38-calibre guns during a target exercise. Note concussion effects on the water surface, and 16 inch (406 mm) gun barrels in varying degrees of elevation.

The primary armament of an Iowa-class battleship is nine 16 inch (406 mm) / 50-caliber Mark 7 naval guns, which are housed in three 3-gun turrets: two forward and one aft in a configuration known as "2-A-1". The guns are 66 feet (20 m) long (50 times their 16 inch bore, or 50 calibers, from breechface to muzzle). About 43 feet (13 m) protrudes from the gun house. Each gun weighs about 239,000 pounds (108 000 kg) without the breech, or 267,900 ponds with the breech. They fire projectiles weighing from 1,900 to 2,700 pounds (850 to 1,200 kg) at a maximum speed of 2,690 ft/s (820 m/s) up to 24 nautical miles (39 km). At maximum range the projectile spends almost 1½ minutes in flight.

Each gun rests within an armored turet, but only the top of the turret protrudes above the main deck. The turret extends either four decks (Turrets 1 and 3) or five decks (Turret 2) down. The lower spaces contain rooms for handling the projectiles and storing the powder bags used to fire them. Each turret required a crew of 94 men to operate. The turrets are not actually attached to the ship, but sit on rollers, which means that if the ship were to capsize the turrets would fall out. Each turret costs US $1.4 million, but this number does not take into account the cost of the guns themselves

The turrets are "three-gun," not "triple", because each barrel can be elevated independently; they can also be 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 noticeable sideways when a broadside is fired.

The guns can be elevated from −5° to +45°, moving at up to 12° per second. The turrets can be rotated about 300° at about four degrees per second and can even be fired back beyond the beam, which is sometimes called "over the shoulder." The guns are never fired directly forward (in the 1980s refit, a satellite up-link antenna was mounted at the bow). To distinguish between the battleship rounds fired from ship to ship the Iowa class used dye bags which allowed the ships crew to determine which rounds belong to which ship. Iowa, New Jersey, Missouri, and Wisconsin were asssinged the colors Orange, Blue, Red and Green, respectively. Within each turret a red stripe on the wall of the turret just inches from the railing marks the boundary of the gun's recoil, providing the crew of each gun turret with a visual reference for the minimum safe distance range.

Cut away of a 16 inch gun turret

When brought into service during World War II the guns had a barrel life of roughly 290 rounds, due in large part to the Nitrated-Cellulose (NC) propellent. After World War II, the Navy switched to smokeless Powder Diphenylamine (SPD), a cooler-burning propellant, which increased the barrel life from 290 rounds to about 350 rounds. This was increased further by the introduction of a titanium dioxide and wax compound known as "Swedish Addative" onboard New Jersey for here tour in Vietnam, and would later be used aboard 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 Equivilent Rounds (FER).

Like most battleships in World War II, the Iowa-class was equipped the Ford Mk 1A Ballistic Computer, a 3,150 lbs rangekeeper designed to direct gunfire on land, sea, and in the air. This analog computer was used to direct the fire from the battleship's big guns, taking into account several factors such as the speed of the targeted ship, the time it takes for a projectile to travel, and air resistants to the shells fired at a target. Although unable to at first, the rangekeepers eventually gained the ability to use radar data to help target enemy ships and land based targets. The results of this advance were telling: the rangerkeeper was able to track and fire at targets at a greater range and with increased accuracy, as was demonstrated in November 1942 when the battleship USS Washington engaged the Imperial Japanese Navy battlecruiser Kirishima at a range of 18,500 yards at night. The engagement left Kirishima in flames, and she was ultimately scuttled by her crew. This 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. 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.

16-inch naval gunfire shells

The large calibur guns were designed to fire two different 16 inch shells: an armor piercing round for anti-ship and anti-structure work, and a high explosive round designed for use against unarmored targets and shore bombardment.

The Mk. 8 APC (Armor-Piercing, Capped) shell weighs in at 2,700 lb (1225 kg) and was designed to penetrate the hardened steel armor carried by foreign battleships. At 20,000 yards (18 km) the Mk. 8 could penetrate 20 inches (500 mm) of steel armor plate. At the same range, the Mk. 8 could penetrate 21 feet (6.4 m) of reinforced concrete. For unarmored targets and shore bombardment, the 1,900 lb (862-kg) Mk. 13 HC (High-Capacity—referring to the large bursting charge) shell was available. The Mk. 13 shell would create a crater 50 feet (15 m) wide and 20 feet (6 m) deep upon impact and detonation, and could defoliate trees 400 yards (360 m) from the point of impact.

The final type of ammunition developed for the Iowa class were "Katie" shells. These shells were born from the nuclear deterance that had begun to shape the United States armed forces as the Cold War began. To compete with the Air Force and the Army, which had developed nuclear bombs and nuclear shells for use on the battlefield the United States Navy began a top-secret program to develop Mk. 23 nuclear naval shells with an estimated yield of 15 to 20 kilotons. These shells were designed to be launched from the best seaborne artillery platform available, which at the time were the four ships of the Iowa class. The shells entered development around 1953, and were reportedly ready by 1956; however, it is not known whether they were ever actually deployed on the Iowa-class battleships because the United States Navy does not confirm or deny the presence of nuclear weapons aboard its ships. In 1991 the U.S. unilaterally withdrew its nuclear artillery shells from service, and Russia responded in kind in 1992. The U.S. removed around 1,300 nuclear shells from Europe and reportedly dismantled its last shells by 2003.

Secondary battery

A 5 inch (127 mm) gun mount emblazened with the Eagle, Globe, and Anchor of the United States Marine Corps aboard the battleship New Jersey

The secondary battery of the ship consists of 5 inch (127 mm) / 38-caliber guns in a series of twin mounts. These guns were introduced in 1934 for use on destroyers, but by the time of World War II they had been installed on nearly every major warship in the US fleet. Originally the secondary battery was intended to be part of the anti-aircraft defenses, but as aircraft became faster their effectiveness in that role decreased. Their use increased again toward the end of the war through a combination of the Mark 37 Fire Control System and the development of proximity-fuzzed 5 inch shells that burst near the target rather than requiring a direct hit. By the time of the Gulf War the secondary battery was largely relegated to shore bombardment and littoral defense. Until the modernization in the 1980s there were ten twin mounts, five on each side of the ship. In the modernization the two mounts farthest aft on each side were removed to make room for missiles, leaving the ship with just six twin mounts.

Each gun cost roughly US $100,000 per gun assembly, which does not include the cost of the mounting. The guns weigh 3,990 lbs. (1,810 kg) without breech, and each gun mount was capable of holding 450 rounds of ammunition. Depending on the mount, a 5"/38 caliber gun could have a crew of up to 13 which are drawn from the sailors serving aboard the ship. Since all four Iowa class ships carried a detachment of United States Marines the Marines manned one of the 5 inch mounts. This mount was usually decorated with the Eagle, Globe, and Anchor, the official Marine emblem. The 5 inch guns on the Iowa class battleships have an effective range of 9 miles (14 km) and can be fired as fast as the crew can load and fire them. A good crew could run 16 to 23 rounds per minute through them.

Anti-aircraft batteries

Since they were designed to escort the U.S. fleet of fast attack aircraft carriers the Iowa-class battleships were all intended to carry a fearsome array of anti-aircraft guns to protect U.S. aircraft carriers from Japanese fighters and dive bombers.

Oerlikon 20 mm anti-aircraft guns

An Oerlikon 20mm anti-aircraft gun aboard the battleship USS Iowa.

The Oerlikon 20mm anti-aircraft gun was one of the most heavily produced anti-aircraft guns of the Second World War; The US alone manufactured a total of 124,735 of these guns. When activated in 1941 these guns replaced the 0.50"/90 (12.7 mm) M2 Browning MG on a one-for-one basis. The Orelikon 20 mm AA gun remained the primary anti-aircraft weapon of the United States Navy until the introduction of the 40 mm Bofors AA gun in 1943.

These guns are air-cooled and use a gas blow-back recoil system. Unlike other automatic guns employed during World War II the barrel of the 20 mm Orelikon gun does not recoil, the breechblock is never locked against the breech and is actually moving forward when the gun fires. This weapon lacks a counter-recoil brake, as the force of the counter-recoil is checked by the explosion of the next round of ammunition.

Between December 1941 and September 1944, 32% of all Japanese aircraft downed were credited to this weapon, with the high point being 48.3% for the second half of 1942. In 1943 the revolutionary Mark 14 Gunsight was introduced which made these guns even more effective; however, the 20 mm guns were found to be inefective against the Japanese Kamikaze attacks used during the latter half of World War II. They were subesquently phased out in favor of the heavier 40 mm Bofors AA guns.

Bofors 40mm anti-aircraft guns

Bofors 40 mm anti-aircraft guns on a MK 12 quadruple mount fire from the deck of the USS Hornet in World War II.

Arguably the best heavy anti-aircraft weapon of World War II, the Bofors 40mm anti-aircraft gun was used on almost every major warship in the US and UK fleet during World War II from about 1943 to 1945. Although a descendent of German and Swedish designs, the Bofors mounts used by the United States Navy during World War II had been heavily "Americanized" to bring the guns up to the standards placed on them by the US Navy. This resulted in a guns system set to English standards (now known as the Standard System) with interchangeable ammunition, which simplified the logistics situation for World War II. When coupled with hydraulic couple drives to reduce salt contamination and the Mark 51 director for improved accuaracy the Bofors 40mm gun became a fearsome adverary, accounting for roughly half of all Japanese aircraft shot down between 1 October 1944 and 1 February 1945.

When the Iowa-class battleships were launched in 1943 and 1944 they carried twenty quad Bofors 40 mm gun mounts, which they used for defense against enemy aircraft. These heavy guns were also employed in the protection of allied aircraft carriers operating in the Pacific Theatre of World War II. These guns remained on the battleships from the time they were commissioned until they were reactivated for service in the 1980s. As each battleship arrived for modernization during the early and mid 1980s the Bofors mounts that remained aboard the battlewagons were removed due in large part to their ineffectiveness against modern day jet fighters and the lack of proctection the Bofors affords against enemy missiles. The replacement for the Bofors guns was the US Navy's Phalanx Close-in weapon system (CIWS).

Phalanx CIWS

A Phalanx CIWS mount aboard the amphibious assault ship USS Kearsarge.

During their modernization in the 1980s each Iowa-class battleship was equipped with four of the United States Navy's Phalanx CIWS mounts, two which sat just behind the bridge and two which were fixed to a platform installed between the ship's funnels. Iowa, New Jersey, and Missouri were equipped with the Block 0 version of the Phalanx, while Wisconsin received the first operational Block 1 version in 1988.

Developed as the final line of defense (terminal defense or point defense) against anti-ship missiles, the Phalanx Close in Weapon System (CIWS, pronounced "see-whiz") is the currently used anti-aircraft/anti-missile gun in the United States Navy. Due to their design shape, they have been nicknamed R2D2s, in reference to driod R2-D2 from the Star Wars univers. Designed in the early 1970s by General Dynamics, and currently produced by Raytheon, the Phalanx CIWS mount utalizes a 20 mm M61 Vulcan gatling gun to destroy enemy missiles and aircraft that manage to escape anti-missile and anti-aircraft missiles fired from US based ships.

The Phalanx guns work by using a search radar and a tracking radar to follow target that come within 1 to 1.5 nautical miles. When a taget comes within this range the CIWS mount physical moves to track the target while simultaneously evaluting the target against several preset criteria to determine the next course of action. Depending on whether the target criteria is met, the Phalanx mount may automatically engage the incoming target if it is judged to be hostile in nature, or the system may recommend that the Phalanx operator engage a target.

Phalanx CIWS mounts were used by Missouri and Wisconsin during the 1991 Gulf War; Wisconsin alone fired 5,200 20 mm Phalanx CIWS rounds. Missouri also received Phalanx fire during a "friendly fire" incident in which the Perry-class guided missile frigate USS Jarrett mistook chaff fired off by Missouri for a legitimate target and shot at Missouri. Rounds from this attack struck the ship in the bulkhead above the famed "surrender deck" and bounced off the armour, one round penetrated the foward funnel and passed completely through it, and another round pentrated a bulkhead and embedded in an interior passageway of the ship.

Missiles

During the modernization in the 1980s, three important weapons were added to the Iowa-class battleships. The first was the CIWS anti-aircraft/anti-missile system discussed above. The other two were missiles for use against both land and sea targets. At one point the NATO Sea Sparrow was to be installed on the reactivated battleships; however, it was determined that the system could not withstand the over—pressure effects when firing the main battery.

Tomahawk land attack missile

An Armored Box Launcher equiped to the battleship USS New Jersey.

The BGM-109 Tomahawk Land Attack Missile (TLAM) was first introduced in the 1970s, and entered service with the United States in 1983. Designed as a long-range, all-weather, subsonic cruise missile, the Tomahawk is capable of reaching targets at a much greater range that the 16 inch guns on the Iowa-class ships. When added to the battleships in the 1980s the Tomahawk became the longest ranged weapon carried by the battleships.

Owing to the original 1938 design of the battleships, the Tomahawk missiles could not be fitted to the Iowa-class unless the battleships were physically rebuilt in such a way as to accommodate the missile mounts that would be needed to store and launch the Tomahawks. This reliazation prompted the removal of the anti-aircraft guns previously installed on the Iowas and the removal of four of each of the battleships ten 5"/38 DP mounts. The aft end of the battleships were then rebuilt to accommodate the missile magazines. This resulted in the construction of two separate platforms, one located between the first and second funnel and one located behind the second funnel, to which MK-143 Armored Box Launcher (ABL) canisters could be attached. Each Armored Box Launcher carries four missiles, and each of the battleships were outfitted with eight canisters, enabling the Iowa-class to carry and fire a total of 32 Tomahawk Missiles.

The type of Tomahawk carried by the battleships varies, as there are three basic configurations for the Tomahawk: the Anti-Ship Missile (TASM); the Land-Attack Missile-Conventional (TLAM-C); and the Land-Attack Missile-Nuclear (TLAM-N). Each version is similar in appearance and uses the same airframe body and launcher. The conventional Tomahawk missile can carry a 1,000 lb explosive warhead or submunitions which use the missile body to reach their destination. The nuclear varient carriers a 200 kt W80 nuclear warhead.

The TLAM can be eqipped with an inertial and terrain contour matching (TERCOM) radar guidance package to find a destroy its target. The TERCOM radar uses a stored map reference to compare with the actual terrain to determine the missile's position. If necessary, a course correction is then made to place the missile on course to the target. Terminal guidance in the target area is provided by the optical Digital Scene Matching Area Correlation (DSMAC) system, which compares a stored image of target with the actual target image.

The firing weight of the Tomahawk is 2,650 lbs plus a 550 lb booster. It has a cruising speed of 0.5 Mach and an attack speed of 0.75 Mach. The anti-ship version of the Tomahawk has an operating range of 250 nautical miles (nm) and a maximum range of 470 nm, while the conventional land attack missile version has a maximum range of 675 nm and TLAM-N a maximum range of 1,500 nm.

As part of the 1991 Gulf War, USS Missouri and USS Wisconsin used ABL launchers to fire Tomahawk missiles at Iraqi targets during Operation Desert Storm. Wisconsin served as the Tomahawk Land Attack Missile (TLAM) strike commander for the Persian Gulf, directing the sequence of launches that marked the opening of Operation Desert Storm and firing a total of 24 of her own TLAMs during the first two days of the campaign.

Harpoon anti-ship missile

An Mk 141 Quad cell Launcher aboard the German frigate Bremen

For protection against enemy ships the Iowa class is outfitted with the Harpoon Weapons System. The system consists of four Mk 141 "shock-hardened" quad cell launchers designed to carry and fire the Boeing RGM-84 Harpoon anti-ship missile. Each Harpoon is placed in one of four Mk 141 shock-hardened quad cell canister launchers located alongside the aft stack; eight per side, in two pods of four. The wieght of the Harpoon at firing is 1,530 pounds, which includes a booster weighing about 362 pounds. The cruising speed is 0.87 Mach and the maximum range is 64 nautical miles (nm) in Range and Bearing Launch mode and 85 nm in Bearing Only Launch mode.

When an Iowa class battleship fires a Harpoon Missile, a booster propels the missile away from the ship; after approximately 5 miles, the booster drops away. After the booster is discarded a turbojet engine ignites and propels the missile to the target. The stabilizing and actuator fins which help guide the missile to its target are stored folded in the canister and spring into position after launching. These fins direct the missile to the target through inputs from the AN/SWG-1 Harpoon Fire Control System.

The battleships carry and use the RGM/UGM-84 variants of the Harpoon Missile, which are designed to be fired by surface ships. The version uses a solid-fueled rocket booster in an A/B44G-2 or -3 booster section, which is discarded after burn-out. The maximum range is around 140 km (75 nauitical miles).

After launch, the missile is guided towards the target location as determined by the ship by a three-axis Attitude Reference Assembly (ATA) in an AN/DSQ-44 guidance section. The ATA is less accurate than a full-fledged inertial system, but good enough for Harpoon's range. For stabilization and control, the AGM-84A has four fixed cruciform wings (3x BSU-42/B, 1x BSU-43/B) and four movable BSU-44/B tailfins. The missile flies at a low cruise altitude, and at a predetermined distance from the expected target position, its AN/DSQ-28 J-band active radar seeker in the nose is activated to acquire and lock on the target. The radar switch-on distance can be set to lower or higher values, the former requiring a more precisely known target location but reducing the risk to be fooled by enemy Electronic Counter Measures (ECM).

An alternative launch mode is called Bearing-Only Launch (BOL). In this mode, the missile is launched in the general direction of the target, and its radar activated from the beginning to scan for the target in a +/- 45° sector in front of the flight path. Once a target has been located and the seeker locked, the xGM-84A missile climbs rapidly to about 1800 m before diving on the target in whats known as a "pop-up manoeuver". The 221 kg (488 lb) WDU-18/B penetrating blast-fragmentation warhead (in the WAU-3(V)/B warhead section) is triggered by a time-delayed impact fuze.

When no target can be acquired after radar activation, the Harpoon will self-destruct.