(USS Iowa image). Design of a new class of battleships began in 1938 due to rumors that the Imperial Japanese Navy was working on battleships with a displacement of 46,000 tons, exceeding the 35,000-ton limit set by the 1936 London Treaty. Due to these suspicions, the United States, Great Britain and France agreed to invoke the Escalator Clause of the treaty and in this way to be able to build ships outside the previous restrictions. In March 1938 the General Board issued a requirement for a South Dakota-class battleship capable of a speed of 33 knots and a displacement of 40,000 tons. On these dates the main armament was also evaluated, deciding that the 16-inch (406 mm)/50-caliber Mark 2 naval guns were the most suitable for the new ships. These guns were available after the cancellation of the South Dakota class battleships and Lexington class battlecruisers of the early 1920s.(USS Missouri image). From March to June 1938, seven different designs were presented to comply with the requirement. The designs were divided into two main categories, “slow battleships” and “fast battleships”, with three designs in the first and four in the second category respectively. Designs ranged from ships of 54,300 to 57,500 tons displacement, armed with 406 or 460mm guns and capable of speeds between 27 and 33 knots. Finally, in June 1938 the General Board selected the “fast battleship/June 1938” design to be fully developed and give rise to the new class of battleships. Officially designated the “Iowa class,” the winning design featured a 56,600-ton ship at full load, with a waterline length of 262.12 meters, a power output of 230,000 hp giving it a speed of 33 knots, and a main battery of nine 406/50mm guns mounted in triple turrets.The battleships Iowa (BB-61) and New Jersey (BB-62) were authorized on May 17, 1938, shortly before the final design was approved, and Missouri (BB-63) and Wisconsin (BB-64) were authorized on July 6, 1939. In the summer of 1940, Congress authorized an emergency construction program, for which two more ships of this class were ordered, Illinois (BB-65) and Kentucky (BB-66), although finally they would not be built. Construction of the four ships was assigned as follows: Iowa and Missouri at the New York Navy Yard and Wisconsin and New Jersey at the Philadelphia Navy Yard. The USS Iowa entered service on February 22, 1943, the USS New Jersey on May 23, 1943, the USS Wisconsin on April 16, 1944, and the USS Missouri on June 11, 1944.(USS Wisconsin image). The Iowa-class battleships had a hull designed to be efficient at high speed, They had a bow equipped with a small bulb to improve resistance at high speed, and a cruiser-type stern. Due to their enormous length and fine waterplane these vessels were prone to heave motions in heavy seas. Also, because of their huge and sudden widening of the hull lines forward of Turret I, they always had spray formation problems at high speeds. However, they were very stable and seaworthy ships, and excellent gun platforms.(USS New Jersey image). These battleships had two rudders of 31.6 m2 of area that could move 36.5 degrees on either side of their axis. Thanks to this and the hull design, these ships were very easy to handle in deep water and could make very tight turns with small heels. According to the words of some crew members, at sea these battleships maneuvered like destroyers, although they were slow and complicated to maneuver if the distance between the keel and the bottom was less than 2 meters. These ships had two five-bladed inboard propellers of 5.18 meters in diameter and another two four-bladed outboard propellers of 5.56 meters in diameter.(USS Wisconsin image). Speed was one of the strengths of these ships, and although their top speed was declared at 33 knots at 202 rpm, they reached 35 knots on more than one occasion. The plant propulsion was the most powerful ever installed on a battleship, with a maximum power rating of 212,000 shp, although 230,000 shp were developed on a regular basis. This power plant developed 44,000 shp to maneuver backwards (astern). In addition, special emphasis was placed on the whole set being very compact and as light as possible, with excellent compartmentation and with a good provision for cross-connection of boilers and turbines in case of suffering battle damage.(USS Missouri image). The Iowa class had eight 3 drum express type boilers distributed in four fire rooms with each turbine set installed in a separate engine room. In this way, there was a fire room followed by an engine room, repeated four times. The system was completed with two furnances and double uptakes reaching the machinery a total weight of 4,992 tons and its performance and reliability were superior. The USS Missouri once sailed continuously for 58 days without any notable problem. In addition to the propulsion plant, these battleships had eight turbo generators of 1,250 kW each to service all the electrical installations and some 900 electric motors distributed throughout the ship. In addition, two 250 kw auxiliary diesel generators were installed for emergencies, being able to supply energy to the ship within 7 seconds of the failure of the main generators.(USS Missouri image). The protection of the Iowa class is based on the scheme applied to the South Dakota class, reinforced and improved in some areas to provide a zone of immunity against 1,014 kg AP shells fired by the old 406/45mm gun that ranged from 16,100 at 28,500 meters. Against 1,223 kg AP shells fired by the modern 406/45mm gun, immunity was less, ranging from 18,650 to 24,400 meters.The 307mm thick main side belt armor was superimposed on 22mm STS (special treatment steel) plates. This belt was sloped outboard 19 degrees from the vertical offering the same protection as a 440mm vertical belt. The lower side belt had the same slope as the main one and tapered from 307mm at the top to 41mm at the bottom.(USS New Jersey image). Due to the increasing danger of air attacks, horizontal protection was specially studied in these ships and they had excellent protection. Up to four armored decks were installed in some areas, with special care taken over machinery and magazines areas. The main deck had a thickness of 38mm, the second deck was made up of two 121 + 32mm plates, then there was a 16mm splinter deck (only over machinery) and finally there was the third deck with a thickness ranging from 13 to 16mm over machinery and 25mm over magazines.Iowa class was fitted with a heavily armored three-level conning tower with 444mm side plates, 184mm roof plates and 100mm deck armor. The forward armored bulkhead tapered in thickness from 287mm (368mm on the Missouri and Wisconsin) on the second deck to 216mm on the inner bottom. The aft transverse bulkhead had 287mm thick plates between the second and third decks and access to the steering gear was protected with 343mm thick side plates.(USS Iowa image). The lateral protection scheme has been kept secret but it was based on the South Dakota class, being multi-layered, with at least four layers installed. Much attention was paid to anti-torpedo protection with a well-studied liquid-loaded arrangement in accordance with the experiences of the war. For the first time on an American battleship, side protection was considered as important as shell and bomb protection. In any case, it became clear in the course of the war that the protection against aerial bombs that hit a ship almost vertically was practically nil.(USS New Jersey image). In summary, the Iowa-class battleships had 19,621 tons of armor, which was 42.77% of the total light ship displacement. This percentage was slightly higher than the North Carolina class (42.34%) but considerably higher than the South Dakota class predecessors (39.63%). Based on these data, it can be said that these battleships were the best protected in the entire history of the US Navy.For these new battleships it was decided to install nine 16-inch (406 mm)/50-caliber Mark 7 naval guns mounted in three “three-gun” turrets. Each gun could be elevated and loaded independently from the others, or fire a full salvo together if necessary. These guns were the most powerful ever fitted to any American ship and were considerably more powerful than the Mark 6 used on earlier battleships, and thanks to a heavier propelling charge and longer barrel, a higher muzzle velocity was achieved which resulted in a longer range and better armor penetration.Each of these guns measured 20.67 meters in length and weighed (including the breech mechanism) 121,515 kg. The breech mechanism was of the down-swing carrier type. The chamber had a length of 2.68 meters and a volume of 442.45 liters. The barrel was rifled and had 96 grooves that ran 17.34 meters inside the barrel. The approximate life of the barrel was about 290 shells and total capacity of the magazines was about 1,220 shells.During WWII these guns used two types of rounds, the 1,225 kg Mk.8 AP (armor-piercing) with a muzzle velocity of 762 m/s and the 862 kg Mk.13/Mk.14 of high-capacity (HC) and a muzzle velocity of 820 m/s, both measuring 1.67 meters in length. The HC shell carried a 69.75 kg burster charge for use in bombardment missions and had a maximum range of 38 km. The normal charge was 6 bags of powder (299.37 kg), but a reduced charge of only 142.8 kg could be used to reduce bore wear. With reduced charge the AP shell had a muzzle velocity of 549 m/s and a maximum range of 22.11 km and the HC shell had a muzzle velocity of 632 m/s and a range of 25 km.The maximum range with AP shells was about 38.70 km, being able to penetrate side plates up to 829mm at 0 meters, 747mm from 4.5 km, 509mm from 18.2 km or 241mm from 38.7 km. Penetration over armor decks was 17mm from 4.5km, 99mm from 18.2km or 357mm from 38.7km. The rate of fire was 2 rounds per minute and the maximum recoil was 1.22 meters. During operations in Vietnam in 1969, Captain Edward Snyder of the New Jersey claimed that AP rounds could penetrate up to 9.72m (32 feet) of reinforced concrete.The 406/50mm Mk.7 guns were mounted in triple turrets designated “16-inch/50-caliber 3-gun turret BB-61 class” which had a weight (without shells) of between 1,728 and 1,735 tons. The maximum training rate was 4 degrees per second and the elevating rate was 12 degrees per second. Minimum and maximum elevations were −5 and 5 degrees respectively. All turrets had 300 degree training arcs and required a minimum of 77 men to operate. Protection consisted of 495mm of armor at the front, 241mm at the sides, 184mm at the roof and 305mm at the rear. The shells were stored two levels below the barbette (2) and raised to the turret by separate elevators than the powder bags. The hatches in the upper and lower barbettes (3) could not be opened simultaneously to prevent contact between the turret and the powder magazines in the event of an explosion. The powder bags were packed in special containers with three bags each (1).During the 1967-68 reactivation of the USS New Jersey the powder bags for firing full charges were modified. The so-called “Swedish additive jackets” were incorporated, which were filled with 1.6kg of titanium dioxide and wax. These jackets were wrapped around the six powder bags in each full charge. The insulating layer formed by this additive drastically reduced bore wear, being 4 times less than without the additive in the case of AP shells. In the case of the HC rounds, the firing of nine of them produced the same wear as a single AP round without additive.Along with the main battery, the Iowas had a powerful secondary battery made up of twenty 127/38mm Mk.12 dual purpose guns in ten twin Mk.28 Mod 2 turrets. These guns fired a 24.43 kg shell with a muzzle velocity of 792 m/s to a maximum range of 16 km against surface targets. The maximum elevation was 85 degrees and the minimum -15 degrees and its effective anti-aircraft range was about 4 km. The life of the barrel was about 4,600 rounds.The armament was completed with the antiaircraft battery, which in the original design had to be composed of twelve 28mm guns and twelve 12.7mm machine guns. Of course, as the war progressed it became clear that this was grossly insufficient and during construction the air defense was increased to eighty 40mm Bofors guns in quad mounts and fifty 20mm Oerlikons guns, although this amount varied in each ship of the class. After this increase, and thanks to their excellent fire-control systems, these battleships were the ones that had the best anti-air defense of all of WWII.Despite its excellent antiaircraft battery, it was not effective enough against Japanese kamikaze attacks, so the possibility of changing part of the quadruple 40mm mounts to twin 76mm mounts was studied, but these changes were not finally implemented. Similarly, the 20mm guns remained unchanged throughout WWII. Each battleship of the class was fitted with two aft steam catapults along with two floatplanes to carry out observation and correction of fire from the 406mm guns and search-and-rescue missions if necessary. The floatplanes on board during WWII were the Curtiss SC Seahawk and Vought OS2U Kingfisher models.Thanks to its late entry into service, the Iowa class had the most modern navigation and fire control radars. At the end of WWII they had an SK air-search radar, later replaced by an SK-2, and an SG radar for surface-search. The 406mm guns were controlled by two Mk.38 or Mk.40 gun fire control systems (GFCS) with Mk.27 or Mk.13 radars. The 127mm guns were controlled by four Mk.37 GFCS with Mk.22 height finding radars and Mk.12 fire control radars. Finally, the 40mm guns were controlled by Mk.56 GFCS with Mk.35 radars. These ships already had electronic countermeasures (ECM) equipment such as the SPT-1 and SPT-4 devices, a pair of DBM radar direction finders, TDY-1 jammers and three intercept receiving antennas. They also had a Mk.III identification, friend or foe (IFF) system and 21 radio transmitters and 65 receivers for voice and CW communications.(USS New Jersey). Entering service late in WWII, the threat from Japanese battleships was viewed as truly distant, so the four ships of the class were assigned to the “Fast Carrier Task Force” for anti-aircraft escort and bombardment missions mainly. All ships operated in the Pacific Theater, although the USS Iowa operated from late August to late October 1943 in the Atlantic in anticipation that the German battleship Tirpitz might enter those waters.(USS Iowa & Missouri image). After the end of WWII, the USS Wisconsin, USS New Jersey and USS Iowa were in service until 1948 (the first two) and 1949 (the last). On these dates they were deactivated and kept in the reserve fleet until 1950-51 when they were reactivated again for participation in the Korean War. However, the USS Missouri operated continuously from her commissioning in June 1944 until her deactivation in late February 1955.(USS Iowa image). Upon being reactivated for the Korean War, the ships were barely modernized and had only minor changes. The two steam catapults were removed and the two floatplanes were replaced by a Sikorsky HO3S-1 helicopter. Likewise, almost all the 20mm guns were withdrawn as they were considered ineffective and expensive to maintain, and some electronic equipment was modernized. The tasks carried out were the same as during WWII and after the end of the operations, the three ships reactivated were sent back to the reserve fleet. The USS New Jersey was deactivated in August 1957 and the USS Iowa and USS Wisconsin were deactivated in February and March 1958 respectively.
