Iowa Class Battleship - Background

Background

Work on what would eventually become the Iowa-class battleships began on the first study in early 1938 at the direction of Admiral Thomas C. Hart, head of the General Board. It was an expanded South Dakota, carrying either twelve 16-inch/45 caliber Mark 6 guns or nine 18-inch (460 mm) guns—the latter armament being dropped after the 31 March agreement—with more armor and a power plant large enough to drive the larger ship through the water at the same speed as the South Dakotas, 27 knots (50 km/h; 31 mph). These studies had no further impact on the design of the Iowa class, but development of this design continued and eventually evolved into the design for the Montana class.

Another design, pursued by the Design Division section of the Bureau of Construction and Repair, was a "cruiser-killer." Beginning on 17 January 1938 under Captain A.J. Chantry, the group drew up plans for ships with twelve 16-inch and twenty 5-inch guns, Panamax capability but otherwise unlimited displacement, a top speed of 35 knots (65 km/h; 40 mph) and a range of 20,000 nautical miles (37,000 km; 23,000 mi) when traveling at the more economical speed of 15 knots (28 km/h; 17 mph). Their plan fulfilled these requirements with a ship of 50,940 long tons (51,760 t), but Chantry believed that more could be done if the ship were to be this large; with a displacement greater than that of most battleships, its armor would only have protected it against the 8-inch (203 mm) weapons carried by heavy cruisers.

Three improved plans—"A", "B", and "C"—were designed at the end of January. An increase in draft, vast additions to the armor, and the substitution of twelve 6-inch (150 mm) guns in the secondary battery was common between the three designs. "A" was the largest, at 59,060 long tons (60,010 t), and was the only one to still carry the twelve 16-inch guns in four triple turrets. It required 277,000 shaft horsepower (shp) to make 32.5 knots (60.2 km/h; 37.4 mph). "B" was the smallest at 52,707 long tons (53,553 t); like "A" it had a top speed of 32.5 knots, but "B" only required 225,000 shp to make this speed. It also carried only nine 16-inch guns, in three triple turrets. "C" was similar but it added 75,000 shp (for a total of 300,000 shp), to make the original requirement of 35 knots. The weight required for this and a longer belt—512 feet (156 m), compared with 496 feet (151 m) for "B"—meant that the ship was 55,771 long tons (56,666 t).

In March 1938, the General Board followed the recommendations of the Battleship Design Advisory Board, which was composed of the naval architect William Francis Gibbs, William Hovgaard (then president of New York Shipbuilding), John Metten, Joseph W. Powell, and the long-retired Admiral and former Chief of the Bureau of Ordnance Joseph Strauss. The board requested an entirely new design study, focusing on increasing the size of the 35,000 ton South Dakota class. The first plans made for this indicated that 30 knots (35 mph; 56 km/h) was possible on a displacement of about 37,600 long tons (38,200 t). 33 knots (38 mph; 61 km/h) could be bought with 220,000 shaft horsepower and a displacement of around 39,230 long tons (39,860 t), which was well below the treaty's maximum limit of 45,000 long tons (46,000 t).

These designs were able to convince the General Board that a reasonably well-designed and balanced 33-knot (61 km/h) battleship was possible within the terms of the "escalator clause". However, further studies revealed major problems with the estimates. The speed of the ships meant that more freeboard would be needed both fore and amidships, the latter requiring an additional foot of armored freeboard. Along with this came the associated weight in supporting these new strains: the structure of the ship had to be reinforced and the power plant enlarged to avoid a drop in speed. In all, about 2,400 long tons (2,400 t) had to be added, and the large margin the navy designers had previously thought they had—roughly 5,000 long tons (5,100 t)—was suddenly vanishing.

With the additional displacement, the General Board was incredulous that a tonnage increase of 10,000 long tons (10,000 t) would only allow the addition of 6 knots (11 km/h; 6.9 mph)s over the South Dakotas. Rather than retaining the 16"/45 caliber Mark 6 gun used in the South Dakotas, they ordered that future studies would have to include the more powerful (but heavier) 16"/50 caliber Mark 2 guns left over from the canceled Lexington-class battlecruisers and South Dakota-class battleships of the early 1920s. It also allowed the draft of the ships to be increased, meaning that the ships could be shortened (lowering weight) and the power reduced (since a narrower beam reduces drag).

The 50-caliber gun weighed some 400 long tons (410 t) more than the 45 caliber did; the barbette size also had to be increased so the total weight gain was about 2,000 long tons (2,000 t), putting the ship at a total of 46,551 long tons (47,298 t)—well over the 45,000 long ton limit. An apparent savior appeared in a Bureau of Ordnance preliminary design for a turret that could carry the 50 caliber guns in a smaller barbette. This breakthrough was shown to the General Board as part of a series of designs on 2 June 1938.

However, the Bureau of Ordnance continued working on a larger barbette design, while the Bureau of Construction and Repair utilized the smaller barbettes in the final planning of the new battleships. As the bureaus were independent of one another, they did not realize that the two plans could not go together until November 1938, when the design was in the final stages of refinement. By this time, the ships could not use the larger barbette, as it would require massive alterations to the design and would result in substantial weight penalties. The General Board was astounded; one member asked the head of the Bureau of Ordnance if it had occurred to him that Construction and Repair would have wanted to know what turret his subordinates were working on "as a matter of common sense". A complete scrapping of plans was only avoided when designers within the Bureau of Ordnance were able to design a new 50-caliber gun, the Mark 7, that was both lighter and smaller in outside diameter; this allowed it to be placed in a turret that would fit in the smaller barbette. The redesigned 3-gun turret, equipped as it was with the Mark 7 naval gun, provided an overall weight saving of nearly 850 long tons (860 t) to the overall design of the Iowa class.

In May 1938 the United States Congress passed the Second Vinson Act which "mandated a 20% increase in strength of the United States Navy". The act was sponsored by Carl Vinson, a Democratic Congressman from Georgia who was Chairman of the House Naval Affairs and Armed Services Committee. The Second Vinson Act updated the provisions of the Vinson-Trammell Act of 1934 and the Naval Act (1936), which had "authorized the construction of the first American battleships in 17 years", based on the provisions of the London Naval Treaty of 1930; this act provided the funding to build the Iowa class.

As 1938 drew to a close the design of the Iowas was nearly complete, but it would continuously evolve as the battleships were under construction. These revisions included changing the design of the foremast, replacing the original 1.1"/75-caliber guns that were to be used for anti-aircraft work with 20 mm and 40 mm guns, and moving the combat information center into the armored hull. Additionally, in November 1939 the New York Navy Yard greatly modified the internal subdivision of the machinery rooms, as tests had shown the underwater protection in these rooms to be inadequate. The result of this was clearly beneficial: "The prospective effect of flooding was roughly halved and the number of uptakes and hence of openings in the third deck greatly reduced." Although the changes meant extra weight and added 1 foot (0.30 m) to the beam, this was no longer a major issue; the United Kingdom and France had renounced the Second London Naval Treaty soon after the beginning of the Second World War.

For half a century prior to laying down, the U.S. Navy had consistently advocated armor and firepower at the expense of speed. Even in adopting fast battleships of the North Carolina class, it had preferred the slower of two alternative designs. Great and expensive improvements in machinery design had been used to minimize the increased power on the designs rather than make extraordinary powerful machinery (hence much higher speed) practical. Yet the four largest battleships the U.S. Navy produced were not much more than 33-knot versions of the 27-knot, 35,000 tonners that had preceded them. The Iowas showed no advance at all in protection over the South Dakotas. The principal armament improvement was a more powerful 16-inch gun, 5 calibers longer. Ten thousand tons was a very great deal to pay for 6 knots.