USS Illinois (BB-65) - Design

Design

The passage of the Second Vinson Act in 1938 had cleared the way for construction of the four South Dakota-class battleships and the first two Iowa class fast battleships (those with the hull numbers BB-61 and BB-62). The latter four battleships of the class, those designated with the hull numbers BB-63, BB-64, BB-65, and BB-66 were not cleared for construction until 1940, and at the time BB-65 and BB-66 were intended to be the first ships of the Montana-class.

Originally, BB-65 was to be the United States Navy's counter to the Empire of Japan's Yamato-class battleships, whose construction at the time was known to the highest-ranking members of the United States Navy, along with the rumors that the Yamato-class ships would carry guns of up to 18 in (460 mm). To combat this, the United States Navy began designing a 58,000 ton ship with an intended armament of twelve 16 in (410 mm) guns. This battleship took shape in the mid-1930s as USS Montana, the lead ship of her class of dreadnought battleships. She would have fielded three more 16 in (410 mm) guns than those mounted aboard the Iowa-class, a more powerful secondary battery of 5 in (130 mm)/54 caliber Mark 16 dual purpose mounts, and an increase in armor designed to enable Montana to withstand the effects of enemy guns comparable to her own.

The increase in Montana's firepower and armor came at the expense of her speed and her Panamax capabilities, but the latter issue was to be resolved through the construction of a third, much wider set of locks at the Panama Canal. As the situation in Europe deteriorated in the late-1930s, the USA began to be concerned once more about its ability to move warships between the oceans. The largest US battleships were already so large as to have problems with the canal locks; and there were concerns about the locks being put out of action by enemy bombing. In 1939, to address these concerns, construction began on a new set of locks for the canal that could carry the larger warships which the US had either under construction or planned for future construction. These locks which would have enabled Montana to transit between the Atlantic and Pacific Oceans without the need to sail around the tip of South America. As USS Montana, BB-65 would have been the only battleship class commissioned by the US to approach the Imperial Japanese Navy's Yamato class on the basis of armor, armament, and tonnage.

By 1942 the United States Navy shifted its building focus from battleships to aircraft carriers after the successes of carrier combat in both the Battle of the Coral Sea, and to a greater extent, the Battle of Midway. As a result the construction of the US fleet of Essex-class aircraft carriers had been given the highest priority for completion in the US shipyards by the US Navy. The Essex-class carriers were proving vital to the war effort by enabling the Allies to gain and maintain air supremacy in the Pacific War, and were rapidly becoming the principal striking arm of the United States Navy in the ongoing effort to defeat the Empire of Japan. Accordingly, the United States accepted shortcomings in the armor for their North Carolina-class battleships, South Dakota-class, and Iowa class battleships in favor of additional speed, which enabled these battleship classes to steam at a comparable speed with the Essex-class and provide the carriers with the maximum amount of anti-aircraft protection.