Second London Naval Treaty

[3] However, a so-called "escalator clause" was included at the urging of American negotiators in case any of the countries that had signed the Washington Naval Treaty refused to adhere to this new limit.

The designs of the King George V and North Carolina classes were initiated before the escalator clause was invoked, being intended to be armed with, and protected against, 14-inch guns.

However, the completed vessel was an unbalanced battleship since its armor scheme was not proof against its up-gunned main armament, so no further ships of the North Carolina were ordered.

The four battleships of the South Dakota class were designed with and protected against 16-inch guns, but maintained a 35,000 ton standard displacement, so this necessitated a shorter hull which made for a compact and cramped ship.

No longer limited to the Second London Naval Treaty but still constrained by the need to pass through the Panama Canal, design of the Iowa began in 1938 and its orders were placed in 1939; with improved 16-inch guns and greater speed on a displacement of 45,000 tons.

Also, unarmed merchant vessels which did not demonstrate "persistent refusal to stop...or active resistance to visit or search"[5] could not be sunk without the ships' crews and passengers being first delivered to "a place of safety" (for which lifeboats did not qualify, except under particular circumstances).