During the World War II (1941-1945), the United States Navy grew rapidly. It had the main role in the war against Japan and important role in the war against Italy and Germany. Also, British Royal Navy played the center role in the war in Europe. The production of battleships started in 1937. The first battleship was USS North Carolina. During the time while US was neutral, they increased their Navy. By the end of 1941, the U.S. Navy had 350 combat ships ready, and an equal number was under construction. The sudden attack on Perl Harbor, was a huge hit for the United States Army. But, the Imperial Japanese Navy didn’t destroy any aircraft carriers, so they became the mainstay of the new (rebuilt) fleet.
After the attack on Pearl Harbor, the United States Navy had to change naval doctrine. They started following the emphasis on group of ships as the naval weapon who had the main role. This was Alfred Thayer Mahan emphasis that Imperial Japanese Navy also followed. During the World War II, the United States Navy fought 6 battles against the IJN (Imperial Japanese Navy). They were: the Battle of Okinawa, the Battle of Leyte Gulf, the Battle of Midway, the Battle of the Coral Sea, the Battle of the Philippine Sea and the Attack on Pearl Harbor.
The U.S. Navy was at its peak on V-J Day in 1945. They had: thousands of amphibious, 377 destroyers, 28 aircraft carriers, 23 battleships, over 232 submarines, 71 escort carriers and 72 cruisers. The total count of ships was 6.768. There were included auxiliary and supply ships.