The Battleship USS Iowa

Instead, the Bureau of Ordnance designed a turret and barbette for the new16”/50-cal Mk 7 guns with a diameter almost identical to that installed on the North Carolina and the South Dakota class battleships. Thus, approximately 2 000 tons of displacement were conserved and the design of the battleship would remain within the 45 000 tons limit.

On May 17, 1938 Congress appropriated funds for the construction of the first two ships of the new class of so-called “fast battleships”, which were designated BB-61 Iowa and BB-62 New Jersey. The consecutive two vessels of the same class were appropriated on June 6, 1939, and would be named Missouri (BB-63) and Wisconsin (BB-64). A year later, on July 19, 1940, two more battleships of that class, Illinois (BB-65) and Kentucky (BB-66), were appropriated, but although their construction was started, they were never completed.
The order for the first warship of the class of six new battleships was placed with the New York Navy Yard on July 1, 1939.

3. The characteristics of the battleship USS Iowa

The shape of the battleship Iowa and her sister ships’ hull was decided by two factors. The beam could not exceed 33.5 m (109ft) in order to pass through the locks of the Panama Canal. The other factor was the need to achieve high speed, which meant installing powerful machinery. That required much space, therefore the hulls had to be lengthened and slender in form, especially in the bow section.
The 270.43m (878ft) long, flush deck hull is characterized by a slim bow section with raised and curved stem, while the bulbous bowfoot improves drag characteristics. Its shape and dimensions provide excellent seagoing qualities in the Pacific Ocean even in extreme weather conditions, but they were proved to be relatively poor seaboats in the North Atlantic when operating post war with NATO  fleets. it was those length to beam proportions  that made  a great “pacific” hull that made them unsuitable for prolonged operations in North Atlantic weather systems.
The stern section is arranged in such a way, that the outboard propeller shafts are installed in streamlined fins constituting an integral part of the hull, thus improving stability and integrity of the entire structure. There are twin rudders, 31.59 m²  (102.6 sq ft) each.
The hull has three continuous decks. The main or weather deck, the second deck, which is the principal armoured deck and the third lower deck, which covers the machinery spaces and steering mechanisms. All the lower decks or “platforms”, are not continuous decks, as they are interrupted by the machinery spaces. The third platform deck from the top forms the internal layer of the triple bottom system, which extends from the main battery barbette No. 3 to barbette No. 1.

Propulsion plant
To meet the 33 knot speed requirement the Iowa class battleships had to have  powerful machinery capable of 212 000 HP output. To achieve that goal, four boiler rooms and four engine rooms were installed amidships alternating with each other.. There are two boilers in each of the four boiler rooms, which generate steam for the engine room adjacent to its bulkhead. Exhaust fumes from each boiler are carried by a single uptake trunked by four into two separated massive funnels. The first funnel, located over boiler room No. 2 and faired into the rear of the fore superstructure fire control tower, vents the forward boiler rooms, while the second funnel, located over the engine room No. 3, vents the aft boiler rooms.
The Babcock & Wilcox three drum water tube boilers generate steam at the working pressure of 39.7 kg/cm² and temperature of 454° C, which power four sets of General Electric geared steam turbines with the power output of 53 000 HP each. The turbines could be overloaded by 20%, which generated the power output of approximately 254 000 HP. According to calculations the ship could then exceed the designed speed of 33 knots.
The electrical devices (there are over 900 electrical motors on board the ship!) and lighting installation were designed to operate on 450 V, 60 Hz alternating current provided by eight turbo-generators installed in four pairs of 1250 kW each.

The main battery of the Iowa class battleships consists of nine 406mm 16”/50-calibre, Mark 7 guns. Initially, it was planned to use the existing Mark II guns, but since the Ordnance Bureau submitted a successful design for a turret and barbette that would accommodate the latest Mark 7, yet with dimensions that did not exceed those of the barbettes installed aboard the battleship South Dakota, it was decided to use the latter guns. The guns are mounted in three three-gun turrets, two in super-firing position fore and the third aft.
Technical specifications of the main and secondary battery guns mounted aboard the battleship Iowa.
Parameter    16”(406 mm)/50 Mk 7 gun    5”(127 mm)/38 gun
Gun length oa    20.73 m  67.25ft    4.38 m  14.2ft
Gun weight including breech    121.52 t    1.8 t
Grooves     96    45
Rifling length    17.43 m  56.6ft    3.99  13ft
Groove depth    8.81 mm  .3”    -
Recoil    1.22 m  4ft    -
Projectile weight    1 225 kg, 2,695lbs    24.43 kg  79lbs
Muzzle velocity    762 m/s 2,474ft/s    792 m/s  2,571ft/s