Editing Iowa-class battleship (section)

==Specifications==

=== General characteristics ===
[[File:BB61 MS32-1B.jpg|thumb|USS ''Iowa'' in World War II configuration and wearing [[World War II ship camouflage measures of the United States Navy|Measure 32 Design 1B]] camouflage pattern, c. 1944.]]

The ''Iowa''-class battleships are {{cvt|860|ft|0|in}} long at the waterline and {{cvt|887|ft|3|in}} long overall with a beam of {{cvt|108|ft|2|in}}.{{refn|Individual ship's dimensions vary slightly from design values. ''Iowa'' is {{cvt|859|ft|5+3/4|in|3}} waterline length, {{cvt|887|ft|2+3/4|in|3}} overall length, and {{cvt|108|ft|2+1/16|in|3}} beam. ''New Jersey'' is {{cvt|859|ft|10+1/4|in|3}} waterline length, {{cvt|887|ft|6+5/8|in|3}} overall length, and {{cvt|108|ft|1+3/8|in|3}} beam.{{sfn|Garzke|Dulin|1995|pp=145–146}}{{sfn|Sumrall|1988|p=157}}|group=N}} During World War II, the draft was {{cvt|37|ft|2|in}} at full load displacement of {{cvt|57540|LT}} and {{cvt|34|ft|9+1/4|in|2}} at design combat displacement of {{cvt|54889|LT}}. Like the two previous classes of American fast battleships, the ''Iowa''s have a double bottom hull that becomes a triple bottom under the armored citadel and armored skegs around the inboard shafts.{{sfn|Garzke|Dulin|1995|pp=144–148}} The dimensions of the ''Iowa''s were strongly influenced by speed. When the Second Vinson Act was passed by the United States Congress in 1938, the U.S. Navy moved quickly to develop a 45,000-ton-standard battleship that would pass through the {{cvt|110|ft}} wide [[Panama Canal]]. Drawing on a 1935 [[Empirical relationship|empirical formula]] for predicting a ship's maximum speed based on scale-model studies in flumes of various [[Hull (watercraft)|hull]] forms and [[propeller]]s{{refn|These mathematical formulas still stand today, and they have been used to design hulls for US ships and to predict the speed of those hulls for the ships when commissioned, including [[nuclear power|nuclear-power]]ed ships like the US fleet of {{sclass|Nimitz|aircraft carrier|0}} [[supercarrier]]s.{{sfn|Rogers|n.d.|p=15}}|group=N}} and a newly developed empirical theorem that related [[waterline length]] to maximum beam, the Navy drafted plans for a battleship class with a maximum beam of {{cvt|108|ft|2|in}} which, when multiplied by 7.96, produced a waterline length of {{cvt|860|ft|0}}.{{sfn|Rogers|n.d.}} The Navy also called for the class to have a lengthened [[forecastle]] and amidship, which would increase speed, and a [[bulbous bow]].{{sfn|Rogers|n.d.|p=10}}

The ''Iowa''s exhibit good stability, making them steady gun platforms. At design combat displacement, the ships' (GM) [[metacentric height]] was {{cvt|9.26|ft}}.{{sfn|Garzke|Dulin|1995|pp=144–148}} They also have excellent maneuverability in the open water for their size, while seakeeping is described as good, but not outstanding. In particular, the long fine bow and sudden widening of the hull just in front of the foremost turret contributed to the ships being rather wet for their size. This hull form also resulted in very intense spray formations, which led to some difficulty refueling escorting destroyers.{{sfn|Friedman|1986|p=324}}{{sfn|Garzke|Dulin|1995|pp=272–273, 278–279}}

=== Armament ===
{{main|Armament of the Iowa-class battleship}}

====Main battery====
{{multiple image
| direction= vertical
| width  = 220
| footer =
| image1 = Iowa 16 inch Gun-EN.svg
| alt1   = A multicolor cutaway of a 16in gun turret. Within the cutaway black lines point to various areas and objects of note, at the other end of the black lines English labels are given for identification purposes.
| caption1= Cutaway of a 16"/50 gun turret.
| image2 = Uss iowa bb-61 pr.jpg
| alt2   = An overhead view of a large ship with a teardrop shape firing guns toward the top of the image.
| caption2= {{USS|Iowa|BB-61|6}} fires a full broadside of nine 16-inch and six 5-inch guns during a gunnery exercise (1984)
| image3 = USS Iowa gun load.jpg
| alt3   = A ship deck with blue bullet and six drum shapes lined up behind the bullet
| caption3= 16"/50 gun projectile with six propellant bags (display) aboard USS ''Iowa'' (BB-61)
}}
The primary guns used on these battleships are the nine {{convert|16|in|0|adj=on}}/50-caliber Mark 7 naval guns, a compromise design developed to fit inside the barbettes. These guns fire high explosive- and armor-piercing shells and can fire a 16-inch shell approximately {{convert|23.4|nmi|km mi}}.{{sfn|Thompson|1999|pp=70–81}}<ref name="NavWeaps 16/50">{{Harvard citation no brackets|NavWeaps.com|loc= [http://www.navweaps.com/Weapons/WNUS_16-50_mk7.php 16"/50 Mark 7]}}</ref> The guns are housed in three 3-gun turrets: two forward of the battleship's [[superstructure]] and one aft, in a configuration known as "2-A-1". The guns are {{convert|66|ft}} long (50 times their 16-inch bore, or 50 calibers from [[breechface]] to [[Muzzle (firearms)|muzzle]]). About {{convert|43|ft}} protrudes from the gun house. Each gun weighs about {{convert|239000|lb}} without the breech, or {{convert|267900|lb}} with the breech.<ref name="NavWeaps 16/50" /> They fired {{convert|2700|lb|0|adj=on}} armor-piercing projectiles at a muzzle velocity of {{cvt|2500|ft/s|0|lk=on}}, or {{convert|1900|lb|0|adj=on}} high-capacity projectiles at {{cvt|2690|ft/s|0}}, up to {{convert|24|mi|nmi km}}.{{refn|The actual range of the ''Iowa''-class battleship's 16"/50 caliber guns varies from source to source. The most commonly cited distance for the 16"/50 caliber gun is approximately 20 miles; however, this number does not necessarily take into consideration the age of the gun barrel, the gun barrel's elevation, the projectile variant (armor piercing or high explosive), or the powder charges required to launch the artillery shell, all of which affect the range that a shell fired from a 16"/50 caliber gun can attain. The longest confirmed shot fired against an enemy naval unit using a 16"/50 caliber gun appears to have occurred during the raid against Imperial Japanese Navy units at [[Chuuk Lagoon|Truk Atoll]], when ''Iowa'' straddled a destroyer at 35,700 yards,<ref name="straddle"/> while the longest shot ever fired by a 16"/50 caliber gun in a non-combat situation is alleged to have occurred during an unauthorized naval gunnery experiment conducted 20 January 1989 off the coast of [[Vieques, Puerto Rico]] by ''Iowa''{{'}}s [[Master Chief Petty Officer|Master Chief]] [[Fire Controlman]], Stephen Skelley, and Gunnery Officer, [[Lieutenant commander (United States)|Lieutenant Commander]] Kenneth Michael Costigan, who claimed that one of the 16-inch shells traveled {{convert|23.4|nmi|km|-1}}.{{not in citation given|date=October 2024}} In addition, the standard 20-mile range does not take into account experimental artillery shells that were under consideration for use with the 16"/50 caliber gun in the 1980s, some of which are alleged to have been capable of traveling distances in excess of the often cited 20-mile gun range. One example is the Improved HC shell, which is said to have been test fired from ''Iowa'' at Dahlgren sometime after her 1980s recommissioning and is alleged to have achieved a range of over 51,000 yards.<ref name="NavWeaps 16/50" /> |group=N|name=Distance}} At maximum range, the projectile spends almost {{fraction|1|1|2}}&nbsp;minutes in flight. The maximum firing rate for each gun is two rounds per minute.<ref name="BAW">Poyer, pp. 50–53.</ref>

Each gun rests within an armored turret, 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 between 85 and 110 men to operate.<ref name="NavWeaps 16/50" /> The original cost for each turret was US$1.4&nbsp;million, but this figure does not take into account the cost of the guns themselves.<ref name="NavWeaps 16/50" /> The turrets are "three-gun", not "triple", because each barrel is individually sleeved and can be elevated and fired independently. The ship could fire any combination of its guns, including a [[Broadside (naval)|broadside]] of all nine. The fire control was performed by the Mark 38 Gun Fire Control System (GFCS); the firing solutions were computed with the Mark 8 rangekeeper, an analog computer that automatically receives information from the director and Mark 8/13 fire control radar, stable vertical, ship pitometer log and gyrocompass, and anemometer. The GFCS uses remote power control ([[Glossary of British ordnance terms#RPC|RPC]]) for automatic [[gun laying]].<ref name="Mk38">{{cite web |url=http://www.dustdevil.com/ppl/billgx/mk38.htm  |title=Mark 38 Gun Fire Control System |access-date=2007-08-01 |archive-url = https://web.archive.org/web/20041028050854/http://www.dustdevil.com/ppl/billgx/mk38.htm |archive-date = 2004-10-28}}</ref>

The large-caliber guns were designed to fire two different conventional 16-inch shells: the {{convert|2700|lb|0|adj=on}} Mk 8 "Super-heavy" [[APCBC|APC]] (Armor Piercing, Capped) shell for anti-ship and anti-structure work, and the {{convert|1900|lb|0|adj=on}} Mk 13 high-explosive round designed for use against unarmored targets and shore bombardment.{{sfn|Sumrall|1988|pp=73–76}} When firing the same conventional shell, the 16-inch/45&nbsp;caliber Mark 6 used by the fast battleships of the ''North Carolina'' and ''South Dakota'' classes had a slight advantage over the 16-inch/50&nbsp;caliber Mark 7 gun when hitting deck armor&nbsp;– a shell from a 45&nbsp;cal gun would be slower, meaning that it would have a steeper trajectory as it descended. At {{convert|35000|yd|mi km}}, a shell from a 45&nbsp;cal would strike a ship at an angle of 45.2&nbsp;degrees, as opposed to 36&nbsp;degrees with the 50&nbsp;cal.<ref name="NavWeaps 16/45">{{Harvard citation no brackets|NavWeaps.com|loc= [http://www.navweaps.com/Weapons/WNUS_16-45_mk6.php 16"/45 Mark 6]}}</ref> The Mark 7 had a greater maximum range over the Mark 6: {{convert|23.64|mi}} vs {{convert|22.829|mi}}.<ref group=N name=Distance/><ref name="NavWeaps 16/45" /><ref>{{cite web|url=http://www.combinedfleet.com/baddest.htm |title=Battleship Comparison |publisher=Combinedfleet.com |access-date=2012-08-07}}</ref>

In the 1950s, the W23, an adaptation of the [[W19 (nuclear artillery shell)|W19 nuclear artillery shell]], was developed specifically for the 16-inch guns. The shell weighed {{convert|1900|lb|0}}, had an estimated yield of {{convert|15|to|20|ktonTNT|GJ|lk=in}},{{sfn|Yenne|2005|pp=132–133}} and its introduction made the ''Iowa''-class battleships' 16-inch guns the world's largest [[nuclear artillery]]{{sfn|Polmar|2001|p=490}} and made these four battleships the only US Navy ships ever to have nuclear shells for naval guns.{{sfn|Polmar|2001|p=490}} Although developed for exclusive use by the battleship's guns it is not known if any of the ''Iowa''s actually carried these shells while in active service due to the United States Navy's policy of refusing to confirm or deny the presence of nuclear weaponry aboard its ships.{{sfn|Yenne|2005|pp=132–33}}{{refn|"Military members and civilian employees of the Department of the Navy shall not reveal, report to reveal, or cause to be revealed any information, rumor, or speculation with respect to the presence or absence of nuclear weapons or components aboard any specific ship, station or aircraft, either on their own initiative or in response, direct or indirect, to any inquiry. [...] The Operations Coordinating Board (part of President Eisenhower's National Security Council) established the US policy in 1958 of neither confirming nor denying (NCND) the presence or absence of nuclear weapons at any general or specific location, including aboard any US military station, ship, vehicle, or aircraft."<ref>{{cite web |last=Morgan | first=J.G. Jr. |date=3 February 2006 |title=Release of Information on Nuclear Weapons and on Nuclear Capabilities of U.S. Forces (OPNAVINST 5721.1F N5GP) |publisher=Department of the Navy&nbsp;– Office of the Chief of Naval Operations |location=Washington, DC |pages=1–2 |url=http://www.fas.org/irp/doddir/navy/opnavinst/5721_1f.pdf |access-date=2012-07-02 }}</ref>|group=N|name=Nuclear}} In 1991, the United States unilaterally withdrew all of its nuclear artillery shells from service, and the dismantling of the US nuclear artillery inventory is said to have been completed in 2004.{{sfn|DeVolpi|Minkov|Simonenko|Stanford|2005|p=VA-13}}

====Secondary battery====

[[File:5-inch 38-caliber cropped.jpg|thumb|220px|alt=A grey turret with two gun barrels pointing forward. A black eagle, globe, and anchor insignia has been painted on the side of the turret.|A 5-inch gun mount emblazoned with the [[Eagle, Globe, and Anchor]] of the [[United States Marine Corps]] aboard the battleship {{USS|New Jersey|BB-62|2}}. In keeping with tradition, a 5-inch gun mount on each ''Iowa''-class battleship was manned by the ship's Marine Detachment.]]
The ''Iowa''s carried twenty [[5"/38 caliber gun|{{convert|5|in|0|adj=on}}/38 caliber]] Mark 12 guns in ten Mark 28 Mod 2 enclosed base ring mounts. Originally designed to be mounted upon destroyers built in the 1930s, these guns were so successful that they were added to many American ships during the Second World War, including every major [[Classification society|ship type]] and many smaller warships constructed between 1934 and 1945. They were considered to be "highly reliable, robust and accurate" by the Navy's Bureau of Ordnance.<ref name="NavWeaps 5/38">{{Harvard citation no brackets|NavWeaps.com|loc= [http://www.navweaps.com/Weapons/WNUS_5-38_mk12.php 5&quot;/38 Mark 12]}}</ref>

Each 5-inch/38 gun weighed almost {{convert|4000|lb|kg}} without the breech; the entire mount weighed {{convert|156295|lb|kg}}. It was {{convert|223.8|in|mm}} long overall, had a bore length of {{convert|190|in|mm}}, and a rifling length of {{convert|157.2|in|mm}}. The gun could fire shells at about {{cvt|2500|–|2600|ft/s}}; about 4,600 could be fired before the barrel needed to be replaced. Minimum and maximum elevations were −15 and 85&nbsp;degrees, respectively. The guns' elevation could be raised or lowered at about 15&nbsp;degrees per second. The mounts closest to the bow and stern could aim from −150 to 150&nbsp;degrees; the others were restricted to −80 to 80&nbsp;degrees. They could be turned at about 25&nbsp;degrees per second. The mounts were directed by four Mark 37 fire control systems primarily through remote power control (RPC).<ref name="NavWeaps 5/38" />

The 5-inch/38 gun functioned as a [[dual-purpose gun]] (DP); that is, it was able to fire at both surface and air targets with a reasonable degree of success. However, this did not mean that it possessed inferior anti-air abilities. As proven during 1941 gunnery tests conducted aboard {{USS|North Carolina|BB-55|2}} the gun could consistently shoot down aircraft flying at {{convert|12000|–|13000|ft|mi km}}, twice the effective range of the earlier single-purpose [[5"/25 caliber gun (United States)|5-inch/25 caliber]] AA gun.<ref name="NavWeaps 5/38" /> As Japanese airplanes became faster, the gun lost some of its effectiveness in the anti-aircraft role; however, toward the end of the war, its usefulness as an anti-aircraft weapon increased again because of an upgrade to the Mark&nbsp;37 Fire Control System, Mark 1A computer, and proximity-fused shells.{{sfn|Stillwell|1996|p=256}}{{sfn|Sumrall|1988|p=80}}

The 5-inch/38 gun would remain on the battleships for the ships' entire service life; however, the total number of guns and gun mounts was reduced from twenty guns in ten mounts to twelve guns in six mounts during the 1980s' modernization of the four ''Iowa''s. The removal of four of the gun mounts was required for the battleships to be outfitted with the armored box launchers needed to carry and fire Tomahawk missiles. At the time of the 1991 Persian [[Gulf War]], these guns had been largely relegated to littoral defense for the battleships. Since each battleship carried a small detachment of [[United States Marine Corps|Marines]] aboard, the Marines would man one of the 5-inch gun mounts.{{sfn|Wass|1984|p=27}}

====Anti-air battery====

[[File:40mm-guns-USS-New-Jersey-194412.gif|thumb|left|alt=A man wearing a military uniform with an open shirt sleeping between two double-barreled guns|upright|A 40 mm quadruple gun mount onboard USS ''New Jersey'' in 1944]]

At the time of their commissioning, all four of the ''Iowa''-class battleships were equipped with 20 quad 40&nbsp;mm mounts and 49 single 20&nbsp;mm mounts.{{sfn|Terzibaschitsch|1977|pp=147–53}} These guns were respectively augmented with the Mk&nbsp;14 range sight and Mk&nbsp;51 fire control system to improve accuracy.

The [[Rheinmetall Air Defence|Oerlikon]] {{convert|20|mm|1|adj=on|sp=us}} gun, one of the most heavily produced [[anti-aircraft gun]]s of the Second World War, entered service in 1941 and replaced the [[M2 Browning|{{convert|0.50|in|1|adj=on}} M2 Browning MG]] on a one-for-one basis. 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; however, the 20&nbsp;mm guns were found to be ineffective against the Japanese [[Kamikaze]] attacks used during the latter half of World War II and were subsequently phased out in favor of the heavier Bofors {{convert|40|mm|adj=on|sp=us}} AA gun.<ref name="NavWeaps 20mm/70">{{Harvard citation no brackets|NavWeaps.com|loc= [http://www.navweaps.com/Weapons/WNUS_2cm-70_mk234.php 20&nbsp;mm/70 Oerlikon Marks 2, 3, 4]}}</ref>

When the ''Iowa''-class battleships were commissioned in 1943 and 1944, they carried twenty quad 40&nbsp;mm AA gun mounts, which they used for defense against enemy aircraft. These heavy AA guns were also employed in the protection of Allied aircraft carriers operating in the [[Asiatic-Pacific Theater|Pacific Theater of World War II]], and accounted for roughly half of all Japanese aircraft shot down between 1 October 1944 and 1 February 1945.<ref name="NavWeaps 40mm/56">{{Harvard citation no brackets|NavWeaps.com|loc= [http://www.navweaps.com/Weapons/WNUS_4cm-56_mk12.php 40&nbsp;mm/56 Bofors Mark 1, Mark 2, and M1]}}</ref><ref name="NavWeaps 3/50">{{Harvard citation no brackets|NavWeaps.com|loc= [http://www.navweaps.com/Weapons/WNUS_3-50_mk27-33-34.php 3&quot;/50  Marks 27, 33, and 34]}}</ref>{{refn|In early 1945, the United States Navy determined that these 40&nbsp;mm guns were also inadequate for defense against Japanese kamikaze attacks in the Pacific Theater, and subsequently began to replace the Bofors guns with a [[3"/50 caliber gun|{{convert|3|in|0|adj=on}}/50 caliber gun]] capable of using [[Proximity fuze#CITEREF1946|variable time (VT) charges]].<ref name="NavWeaps 40mm/56" /><ref name="NavWeaps 3/50" /> |group=N}} Although successful in this role against WWII aircraft, the 40&nbsp;mm guns were stripped from the battleships in the jet age&nbsp;– initially from ''New Jersey'' when reactivated in 1968{{sfn|Garzke|Dulin|1995|p=139}} and later from ''Iowa'', ''Missouri,'' and ''Wisconsin'' when they were reactivated for service in the 1980s.{{refn|"As part of their modernizations, the ''Iowa''-class vessels lost their AA batteries in favor of [[Phalanx CIWS|Phalanx Close-In Weapon Systems]] and several of their 5-inch/38cal guns to make room for the launchers for the TLAMs and Harpoons."<ref>{{cite web |url=http://www.nps.gov/nr/feature/july/2012/USS_Wisconsin.pdf |title=National Register of Historic Places Registration Form |author=Nauticus |author-link=Nauticus |publisher=United States Department of the Interior |page=11 |type=Official United States Government Document |access-date=2012-11-28}}</ref>|group=N}}

=== Propulsion ===
{{multiple image
| direction= vertical
| align  = right
| width  = 220
| footer =
| image1 = USS New Jersey engine room controls.jpg
| alt1   = A large panel with many dials. A man works a wheel at the far right end of the image.
| caption1= A crewman operates the ship's throttle in the main engine room aboard ''New Jersey'' (1982)
| image2 = USS New Jersey electrical generators.jpg
| alt2   = A large room with gray machinery visible on the right and gray and orange machinery visible on the left. Three men in light blue shirts and one man in a black shirt are working on the equipment.
| caption2= Crewmen operate the electrical generators in the upper-level engine room aboard ''New Jersey'' (1982)
}}

The powerplant of the ''Iowa''s consists of eight [[Babcock & Wilcox]] boilers and four sets of double reduction cross-compound geared [[steam turbine|turbines]], with each turbine set driving a single shaft. Specifically, the geared turbines on ''Iowa'' and ''Missouri'' were provided by [[General Electric]], while the equivalent machinery on ''New Jersey'' and ''Wisconsin'' was provided by [[Westinghouse Electric Corporation|Westinghouse]].<ref name="IOWA MACHINERY">Preston, p. 259.</ref>{{sfn|Sumrall|1988|pp=135–137}} The plant produced {{cvt|212000|shp}} and propelled the ship up to a maximum speed of {{cvt|32.5|kn}} at full load displacement and {{cvt|33|kn}} at normal displacement.{{refn|The empirical formula permitted a theoretical maximum speed of {{cvt|34.9|kn|1}}. However, the actual maximum speed of the ''Iowa''-class battleships was never verified during World War II as the ships never ran a measured mile at full power; {{cvt|31|kn|1}} was considered the operating speed when bottom fouling and sea state were taken into account.{{sfn|Friedman|1986|p=317}} During 1985 sea trials, ''Iowa'' achieved {{cvt|31.0|kn}} at {{cvt|186260|shp}} and nearly full load displacement of {{cvt|55960|LT}}.<ref>{{cite web |last= Toby |first= A. Steven |date= 23 June 2011 |title= Speed Thrills V |website= NavWeaps.com |url= http://www.navweaps.com/index_tech/tech-104.php |access-date= 20 November 2020}}</ref><ref>{{cite report |last= Stenson |first= Richard J. |date= October 1989 |title= First of Class Trials on USS Iowa (BB-61) Class – Past and Present |url= http://www.navweaps.com/index_tech/tech-104_BB61_Sea_Trial.pdf |publisher= [[Carderock Division of the Naval Surface Warfare Center|David Taylor Research Center]], U.S. Navy |location= Bethesda, Maryland |access-date= 20 November 2020 |via= NavWeaps.com}}</ref> When lightly loaded, ''New Jersey'' achieved {{cvt|35.2|kn}} in shallow waters during machinery trials in 1968.<ref>{{cite web |last= DiGiulian |first= Tony |date= 8 November 1999 |title= Speed Thrills II: Max Speed of the Iowa Class Battleships) |website= NavWeaps.com |url= http://www.navweaps.com/index_tech/tech-029.htm |access-date= 20 November 2020}}</ref>|group=N|name=Speed}} The ships carried {{cvt|8841|LT}} of fuel oil which gave a range of {{cvt|15900|nmi}} at {{cvt|17|kn}}. Two semi-balanced rudders gave the ships a tactical turning diameter of {{convert|814|yard|0}} at {{cvt|30|kn}} and {{convert|760|yard|0}} at {{cvt|20|kn}}.{{sfn|Friedman|1986|p=449}}

The machinery spaces were longitudinally divided into eight compartments with alternating fire and engine rooms to ensure adequate isolation of machinery components. Four [[fire room]]s each contained two M-Type [[boiler]]s operating at {{convert|600|psi|kPa kg/cm2|0|lk=on}} with a maximum superheater outlet temperature of {{cvt|850|°F}}.{{sfn|Sumrall|1988|pp=135–137}}<ref>Stillwell, p. 22.{{Incomplete short citation|date=November 2020}}<!--Ambiguous, there are two Stillwells (1986, 1996) cited in article--></ref> The double-expansion engines consist of a high-pressure (HP) turbine and a low-pressure (LP) turbine. The steam is first passed through the HP turbine which turns at up to 2,100 rpm. The steam, largely depleted at this point, is then passed through a large conduit to the LP turbine. By the time it reaches the LP turbine, it has no more than {{cvt|50|psi|kPa}} of pressure left. The LP turbine increases efficiency and power by extracting the last little bit of energy from the steam. After leaving the LP turbine, the exhaust steam passes into a condenser and is then returned as feed water to the boilers. Water lost in the process is replaced by three evaporators, which can make a total of 60,000 US gallons per day (3 liters per second) of fresh water. After the boilers have had their fill, the remaining fresh water is fed to the ship's potable water systems for drinking, showers, hand washing, cooking, etc. All of the urinals and all but one of the toilets on the ''Iowa'' class flush with salt water in order to conserve fresh water. The turbines, especially the HP turbine, can turn at 2,000 rpm; their shafts drive through reduction gearing that turns the propeller shafts at speeds up to 225 rpm, depending upon the desired speed of the ship.{{sfn|Sumrall|1988|pp=118–119}} The ''Iowa''s were outfitted with four screws: the outboard pair consisting of four-bladed propellers {{cvt|18.25|ft}} in diameter and the inboard pair consisting of five-bladed propellers {{cvt|17|ft|2}} in diameter. The propeller designs were adopted after earlier testing had determined that propeller [[cavitation]] caused a drop in efficiency at speeds over {{cvt|30|kn}}. The two inner shafts were housed in skegs to smooth the flow of water to the propellers and improve the structural strength of the stern.{{sfnm|1a1=Sumrall|1y=1988|1p=138|2a1=Rogers|2y=n.d.|2pp=5–6}}

Each of the four engine rooms has a pair of 1,250&nbsp;kW Ship's Service Turbine Generators (SSTGs), providing the ship with a total non-emergency electrical power of 10,000&nbsp;kW at 450 volts alternating current. Additionally, the vessels have a pair of 250&nbsp;kW emergency diesel generators.{{sfn|Friedman|1986|p=449}} To allow battle-damaged electrical circuits to be repaired or bypassed, the lower decks of the ship have a Casualty Power System whose large 3-wire cables and wall outlets called "biscuits" can be used to reroute power.{{sfn|Garzke|Dulin|1995|pp=142–143}}

===Electronics (1943–69)===
The earliest search radars installed were the SK air-search radar and SG surface-search radar during World War II. They were located on the mainmast and forward fire-control tower of the battleships, respectively. As the war drew to a close, the United States introduced the SK-2 air-search radar and SG surface-search radar; the ''Iowa'' class was updated to make use of these systems between 1945 and 1952. At the same time, the ships' radar systems were augmented with the installation of the SP height finder on the main mast. In 1952, [[AN/SPS-10]] surface-search radar and [[AN/SPS-6]] air-search radar replaced the SK and SG radar systems, respectively. Two years later the SP height finder was replaced by the [[AN/SPS-8]] height finder, which was installed on the main mast of the battleships.{{sfn|Garzke|Dulin|1995|pp=141–142}}

In addition to these search and navigational radars, the ''Iowa'' class were also outfitted with a variety of [[Ship gun fire-control system|fire control radars]] for their gun systems. Beginning with their commissioning, the battleships made use of a pair of [[Ship Gun Fire Control Systems#MK 38 Gun Fire Control System|Mk 38 gun fire control systems]] with Mark 8 fire control radar to direct the 16-inch guns and a quartet of [[Ship Gun Fire Control Systems#MK 37 Gun Fire Control System (GFCS)|Mk 37 gun fire control systems]] with Mark 12 fire control radar and Mark 22 height finding radar to direct the 5-inch gun batteries. These systems were upgraded over time with the Mark 13 replacing the Mark 8 and the Mark 25 replacing the Mark 12/22, but they remained the cornerstones of the combat radar systems on the ''Iowa'' class during their careers.{{sfn|Sharpe|1991|p=732}} The range estimation of these gunfire control systems provided a significant accuracy advantage over earlier ships with optical rangefinders; this was demonstrated off [[Truk Atoll]] on 16 February 1944, when the ''New Jersey'' engaged the {{ship|Japanese destroyer|Nowaki|1940|6}} at a range of {{convert|35700|yd|km nmi}} and [[Salvo|straddled]] her, setting the record for the longest-ranged straddle in history.<ref name="straddle">{{cite web |url=https://www.battleshipnewjersey.org/the-ship/full-history/ |title=Full History - USS New Jersey, The World's Greatest Basttleship |date=28 March 2024 |website= Battleship New Jersey |access-date=28 March 2024 |quote=}}</ref>

In World War II, the electronic countermeasures (ECM) included the SPT-1 and SPT-4 equipment; passive electronic support measures (ESM) were a pair of DBM radar direction finders and three intercept receiving antennas, while the active components were the TDY-1 jammers located on the sides of the fire control tower. The ships were also equipped with the [[identification, friend or foe]] (IFF) [[IFF Mark III|Mark III]] system, which was replaced by the [[IFF Mark X]] when the ships were overhauled in 1955. When the ''New Jersey'' was reactivated in 1968 for the Vietnam War, she was outfitted with the ULQ-6 ECM system.{{sfn|Sumrall|1988|pp=115–119}}

=== Armor ===
[[File:USS New Jersey armor citadel.jpg|thumb|220px|alt=A large gray wall, with an open door visible on the left. To the right, the door way into the ship is visible, revealing several inches of gray armor.|A view of the door and {{convert|17.3|in|mm|adj=on|0}} thick armored [[conning tower]] of the battleship ''New Jersey'']]

Like all battleships, the ''Iowa''s carried heavy armor protection against shellfire and bombs with significant underwater protection against torpedoes. The ''Iowa''s' "[[All or nothing (armor)|all-or-nothing]]" armor scheme was largely modeled on that of the preceding ''South Dakota'' class, and designed to give a [[zone of immunity]] against fire from 16-inch/45-caliber guns between {{convert|18000|and|30000|yd|m mi}} away. The protection system consists of Class A face-hardened [[Krupp cemented armour|Krupp cemented]] (K.C.) armor and Class B homogeneous Krupp-type armor; furthermore, [[special treatment steel]] (STS), a high-tensile structural steel with armor properties comparable to Class B, was extensively used in the hull plating to increase protection.<ref>{{cite web |last= Okun |first= Nathan |date= 2017 |title= Table of Metallurgical Properties of Naval Armor and Construction Materials |website= NavWeaps.com |url= http://www.navweaps.com/index_nathan/metalprpsept2009.htm |access-date= 20 November 2020}}</ref>

The citadel consisting of the magazines and engine rooms was protected by an STS outer hull plating {{convert|1.5|in}} thick and a Class A armor belt {{convert|12.1|in|0}} thick mounted on {{convert|0.875|in|adj=on}} STS backing plate; the armor belt is sloped at 19 degrees, equivalent to {{convert|17.3|in|mm|abbr=on|0}} of vertical class B armor at 19,000 yards. The armor belt extends to the triple bottom, where the Class B lower portion tapers to {{convert|1.62|in}}. The ends of the armored citadel are closed by {{convert|11.3|in|0|adj=on}} vertical Class A transverse bulkheads for ''Iowa'' and ''New Jersey''. The transverse bulkhead armor on ''Missouri'' and ''Wisconsin'' was increased to {{convert|14.5|in|0}}; this extra armor provided protection from raking fire directly ahead, which was considered more likely given the high speed of the ''Iowa''s. The deck armor consists of a {{convert|1.5|in|mm|adj=mid|-thick}} STS weather deck, a combined {{convert|6|in|mm|0|adj=mid|-thick}} Class B and STS main armor deck, and a {{convert|0.63|in|mm|adj=mid|-thick}} STS splinter deck. Over the magazines, the splinter deck is replaced by a {{convert|1|in|adj=on}} STS third deck that separates the magazine from the main armored deck.{{sfn|Friedman|1986|p=314}} The powder magazine rooms are separated from the turret platforms by a pair of 1.5-inch STS annular bulkheads under the barbettes for flashback protection.{{sfn|Friedman|1986|p=314}} The installation of armor on the ''Iowa''s also differed from those of earlier battleships in that the armor was installed while the ships were still "on the way" rather than after the ships had been launched.<ref>Stillwell, p. 15.{{Incomplete short citation|date=November 2020}}<!--Ambiguous, there are two Stillwells (1986, 1996) cited in article--></ref>

The ''Iowa''s had heavily protected main battery turrets, with {{convert|19.5|in|0|adj=on}} Class B and STS face, {{convert|9.5|in|0|adj=on}} Class A sides, {{convert|12|in|0|adj=on}} Class A rear, and {{convert|7.25|in|0|adj=on}} Class B roof. The turret barbettes' armor is Class A with {{convert|17.3|in|0}} abeam and {{convert|11.6|in|0}} facing the centerline, extending down to the main armor deck. The conning tower armor is Class B with {{convert|17.3|in|0}} on all sides and {{convert|7.25|in|0}} on the roof. The secondary battery turrets and handling spaces were protected by {{convert|2.5|in|0}} of STS. The propulsion shafts and steering gear compartment behind the citadel had considerable protection, with {{convert|13.5|in|0|adj=on}} Class A side strake and {{convert|5.6-6.2|in|0|adj=on}} roof.{{sfn|Friedman|1986|p=314}}{{sfn|Garzke|Dulin|1995|pp=144–148}}

The armor's immunity zone shrank considerably against guns equivalent to their own 16-inch/50-caliber guns armed with the Mk 8 armor-piercing shell due to the weapon's increased muzzle velocity and improved shell penetration; increasing the armor would have increased weight and reduced speed, a compromise that the General Board was not willing to make.{{sfn|Friedman|1986|p=314}}

The ''Iowa''s' torpedo defense was based on the ''South Dakota''s' design, with modifications to address shortcomings discovered during caisson tests. The system is an internal "bulge" that consists of four longitudinal torpedo bulkheads behind the outer hull plating with a system depth of {{convert|17.9|ft|2}} to absorb the energy of a torpedo warhead. The extension of the armor belt to the triple bottom, where it tapers to a thickness of {{convert|1.62|in}}, serves as one of the torpedo bulkheads and was hoped to add to protection; the belt's lower edge was welded to the triple bottom structure and the joint was reinforced with buttstraps due to the slight knuckle causing a structural discontinuity. The torpedo bulkheads were designed to elastically deform to absorb energy and the two outer compartments were liquid loaded in order to disrupt the gas bubble and slow fragments. The outer hull was intended to detonate a torpedo, with the outer two liquid compartments absorbing the shock and slowing any splinters or debris while the lower armored belt and the empty compartment behind it absorb any remaining energy. However, the Navy discovered in caisson tests in 1939 that the initial design for this torpedo defense system was actually less effective than the previous design used on the ''North Carolina''s due to the rigidity of the lower armor belt causing the explosion to significantly displace the final holding bulkhead inwards despite remaining watertight. To mitigate the effects, the third deck and triple bottom structure behind the lower armor belt were reinforced and the placement of brackets was changed.{{sfn|Friedman|1986|p=285}}{{sfn|Garzke|Dulin|1995|p=93}} ''Iowa''s' system was also improved over the ''South Dakota''s' through closer spacing of the transverse bulkheads, greater thickness of the lower belt at the triple bottom joint, and increased total volume of the "bulge".{{sfn|Jurens|Morss|2016|pp=289–294}}<ref>{{cite journal|last1=Wright|first1=Christopher C.|title=Question 14/56: Concerning a notch in the hull at the top of the Main Deck level, port side, on BB-58|issn=0043-0374 |journal=Warship International |date=September 2020 |volume=LVII |issue=3 |pages=226–237}}</ref> The system was further modified for the last two ships of the class, ''Illinois'' and ''Kentucky'', by eliminating knuckles along certain bulkheads; this was estimated to improve the strength of the system by as much as 20%.{{sfn|Sumrall|1988|pp=132}}

Based on costly lessons in the Pacific theater, concerns were raised about the ability of the armor on these battleships to withstand aerial bombing, particularly high-altitude bombing using armor-piercing bombs. Developments such as the [[Norden bombsight]] further fueled these concerns. While the design of the ''Iowa''s was too far along to adequately address this issue, experience in the Pacific theater eventually demonstrated that high-altitude unguided bombing was ineffective against maneuvering warships.{{sfnm |1a1=Garzke|1a2=Dulin|1y=1995|1p=141 |2a1=Lyon|2a2=Moore|2y=1978|2p=240}}

=== Aircraft (1943–69) ===
When they were commissioned during World War II, the ''Iowa''-class battleships came equipped with two [[aircraft catapult]]s designed to launch [[floatplane]]s. Initially, the ''Iowa''s carried the [[Vought OS2U Kingfisher]]<ref name="Stillwell 62.1">Stillwell, p. 296.{{Incomplete short citation|date=November 2020}}<!--Ambiguous, there are two Stillwells (1986, 1996) cited in article--></ref> and [[Curtiss SC Seahawk]],<ref name="Stillwell 62.1" />{{sfn|Bridgeman|1946|pp=221–22}} both of which were employed to spot for the battleship's main gun batteries&nbsp;– and, in a secondary capacity, perform search-and-rescue missions.

By the time of the Korean War, helicopters had replaced floatplanes and the [[Sikorsky H-5|Sikorsky HO3S-1]] helicopter was employed.<ref name="Stillwell 62.1" /> ''New Jersey'' made use of the [[Gyrodyne QH-50 DASH]] drone for her Vietnam War deployment in 1968–69.{{sfn|Polmar|2001|p=127}}