Editing Iowa-class battleship (section)

====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}}