The Battleship USS Iowa

Thus, finding the golden mean was necessary. Installing the side armour within the hull  sloped at the angle of 19 degrees outwards turned out to be an excellent idea. It allowed an increase the armour thickness by only 6 mm (.2”) and at the same time retain the resistance against 406 mm (16”) projectile hits. Design of the propulsion plant incorporated the latest achievements of marine engineering, which resulted in a more compact machinery space. Trunking of all uptakes allowed design of a compact superstructure with a single funnel and that in turn shortened the length of the entire armoured citadel.
Although it was impossible to meet the designed displacement of 35 000 standard tons the battleship design thus created had exceptional technical characteristics. The four battleships of the South Dakota class built to those specifications turned out to be most successful.
2. Design and construction of the battleship Iowa
When, in autumn of 1937, first Naval Intelligence reports about the first new generation battleship being laid down at Kure Japan, reached the United States, there were serious doubts that the new battleships which were being designed for the US Navy would be a worthy adversary for the new Japanese ships. Although the detailed technical specifications of the Nagato class battleships built in the 1920s and refitted in the second half of the 1930s were not known, they were considered to be well-designed. Their characteristics well exceeded those of any contemporary US designs. Therefore, it was assumed that the Japanese had began construction of an even more modern and powerful warship that the Nagato class.
It was thought apparent that the South Dakota class battleships would not be a match for the new Japanese battleship design.
Since Japan provided non-committal replies to questions concerning the new battleships, Great Britain, France and the United States invoked the escalation clause added to the London Naval Treaty and increased displacement limit for new battleships from 35 000 to 45 000 standard tons.
With additional 10 000 tons at their disposal, American designers could either increase the armour thickness and the armament of the new battleships, or their speed. Numerous concepts and designs were created, but finally, the concept of a fast battleship won, although the specifications were not exceedingly increased. The armament would remain as nine 406 mm (16”) guns with speed increased to 33 knot, within displacement limit of 45 000 standard tons. The design of the South Dakota class battleships was a starting point. It was calculated that a 220 000 HP propulsion plant, which would guarantee speed of 33 knots, required a hull no longer than 240 metres (779ft) and standard displacement would be approximately 40 000 tons. However, because the maximum beam could not exceed 33.5 m, (109ft) in order to allow for passage through the locks of the Panama Canal, the hulls of the new warships had to be lengthened.
The decision to choose a design of a “fast battleship” seems to be obvious by today’s standards, but in the late 1930s it was not so.  At that time, it was difficult to predict whether naval strategy drawn up by Naval staff and high ranking officers, whose experience was that of the World War I, in which the battle fleet had been seen as a major tool for solving naval conflicts was correct, or if  long-term thinking  involving naval aviation was a better option. The primary concern was, whether new carrier-borne aircraft and aircraft carriers could/would be able to play a decisive role in the future naval conflict.
Aircraft carriers were fast warships, but none of the battleships launched before the “building holidays” and then commissioned in the US Navy was capable of serving as their escort, even after modernization. Therefore, the idea of building a few or even a dozen modern, and above all, fast battleships that would be able to keep up with fleet aircraft carriers was rather obvious. Especially in the face of intelligence reports about the modernization of the Japanese Kongo class battleships, which were then able to steam at 32 knots,  effectively capable of serving as a very powerful aircraft carrier escort. Actually, these considerations took precedence and became a deciding factor in the approval of a class of fast battleships.
It is worthy of mention, that there were plans to arm the new battleships with 457 mm (18”) guns. However, preliminary calculations proved that, due to their massive weight, the number would have to be reduced from nine to six. Even then, displacement would be considerably increased and the ships would certainly not be able to exceed the speed of 21 to 23 knots. Ultimately, the new ships’ main battery layout would be similar to that of the South Dakota class battleships, consisting of nine 406 mm (16”) guns mounted in three triple turrets.
Since there was a large number of 406 mm (16”)/50 calibre Mark II guns available from inventory, which had been manufactured for the cancelled Lexington class battlecruisers and never built South Dakota2 class battleships, there was a proposal to mount them in the turrets of the new, fast battleships. However, there was a problem, since their more powerful recoil required longer turrets than those designed for the South Dakota class. Moreover, it turned out that a longer and therefore more spacious turret required a larger diameter barbette, which was out of the question in the situation when each saved ton of the displacement could have been used to improve other characteristics of the ship.