The Battleship USS Iowa

The battleship’s secondary comprising 20 127mm 5”/38-calibre, 1934 pattern Mark 12 guns mounted in ten Mark 28 twin turrets could provide anti-aircraft fire at elevations up to 85 degrees, in addition to anti ship defence.
The designed layout of the anti-aircraft armament was altered during the course of the battleship’s construction. The planned 28 mm 1.1” anti-aircraft guns were not mounted and in their place the more effective quadruple 40 mm Bofors gun mounts were installed. When the ship commissioned in 1943, there was a total of sixty 40 mm guns mounted on board. The anti-aircraft battery was supplemented by 60 very effective 20 mm Oerlikon guns installed in 1943 after commissioning.

Armour protection
The armour protection scheme of the Iowa class battleships was modelled on the proven system used on the battleship South Dakota. The side or belt armour, installed within the hull, is inclined at 19 degrees to the ship’s axis of symmetry, which would protect the battleships against 406mm 16” projectile hits. It is 11.74m
38ft wide and stretches between frame 50 forward of No.1 barbette to frame 166 aft of No.3 barbette. It is 307mm 12” thick in its upper portion, but tapers downwards to only 41mm 1.6”. The lower lip touches the double bottom, which in practice would serve as protection against diving projectiles. The armoured citadel is enclosed by the fore and aft transverse armoured bulkheads.
The horizontal armour consists of the 38mm 1.5” thick main deck and 121mm
4.8” thick second deck, which is the main armoured deck that protected the ship’s vitals against aerial bomb hits. The third deck was only 16mm .6” thick. The details of the main battery turrets and other components of the armour protection scheme are presented in a table.
Underwater protection
The underwater protection scheme of the Iowa class battleships consisted of the series of bulkheads and tanks between them, which were created by the outer plating and three consecutive longitudinal bulkheads. Two outer tanks could be filled with fuel or ballast water. Two inner ones would remain empty. The liquid-filled tanks were to absorb the energy of torpedo explosion, the third, empty tank was to prevent hull leaks, while the fourth, also empty, tank served as protection of the machinery spaces.
The bottom of the hull was protected by the inner bottom stretching between the longitudinal anti-torpedo bulkheads at the entire length of the ship. The double bottom was a storage area for the drinking and process water supplies, as well as the fuel reserve. The space between the second and third bottom always remained empty. The purpose of the triple bottom system was similar to that of the anti-torpedo bulkheads; it was to absorb the shock of underwater explosions.

Technical specifications of the battleship USS Iowa (1943-1945)
Displacement:    43 875 t (light)
48 425 t (standard)
55 424 t (optimum battle)
57 540 t (full load)
59 331 t (maximum)
Length    270,427m  878ft oa
262,689m 852.8ft on waterline
Beam    32,971m 107ft maximum
Draft

      8,744m  28.4ft – at 43 875 t.
10,687m 34.7ft– at 55 424 t.
11,030m  35.8ft – at 57 540 t.
11,328m 36.8ft – at 59 331 t.
11,506m 37.4ft max.
Propulsion    8 Babcok & Wilcox boilers, 4 General Electric geared steam turbines with combined output of 212 000 HP
two 5.182m 16.8ft diameter five blade propellers (inboard)
two 5.563m 18ft diameter four blade propellers (outboard)
Speed    33.0 kn (designed)
Endurance    15 000 NM at 15 kn
Fuel capacity    8 624 t
Armament    nine 406 mm 16/50 Mk 7 guns (3 x 3)
twenty 127 mm 5”/38 Mark 12 guns (10 x 2)
sixty 40 mm Bofors anti-aircraft guns (15 x 4)
sixty 20 mm Oerlikon anti-aircraft guns(60 x I)
December 1944:
Eighty 40 mm Bofors anti-aircraft guns (20 x 4)
Fifty-two 20 mm Oerlikon anti-aircraft guns (52 x I)
Armour    Belt – 307/307 – 41mm 12” - 1.6”
Steering gear – 343mm 13.5”
Armoured decks – 38mm 1.2”, 121mm 4.8”, 16 mm .6”
Main battery turrets – face 432mm 17”, sides 241mm 9.5”, rear 305mm 12”, roof 184mm 7.2”.
Barbettes – 439 – 295mm, 17.2” - 11.6”
Armoured conning tower – 439mm 17.2”,  184mm roof  184mm 7.2”
Communication shafts – 406mm 15.9”
Complement    117 officers and 1 804 sailors (1943)
151 officers and  2 637 sailors (1945)

Operational history