WWII: annual production of major naval vessels 1939-1945, by country

The first half of the 20^th century saw a dramatic shift in naval warfare and the types of ships that were used in conflict at sea.

Changing nature of naval warfare

In 1906, the HMS Dreadnought battleship revolutionized naval warfare, as it was steam powered, incredibly fast for its size, quickly built, and its primary battery of guns was mounted on the main deck. The HMS Dreadnought then inspired virtually all battleships that came after it, in what would become a naval arms race, but as technology advanced in the interwar period, some proposed that aircraft carriers should become the most important ships in the navy. While the attack on Pearl Harbor would highlight the effectiveness of naval air power, and battleships themselves were among the primary targets in the attack, it was not until 1942 at battles such as Midway or the Battle of the Coral Sea where the aircraft carrier established itself as the heart of the navy. Battleships, as well as cruisers or destroyers, largely played a supporting role for the remainder of the war, and (apart from two events) major naval battles became a thing of the past after WWII.

Ascendancy of the U.S. Navy 

Another significant development of WWII was the emergence of the United States as the world's foremost naval power. During the war, the U.S. built almost 9,000 war vessels (not including landing vessels), which was more than three times the amount of all other powers combined. U.S. production capacity meant that it was able to continually produce and replace major vessels as the war waged on. In contrast, the Japanese did not have the ability to replace lost or damaged ships, which contributed to their eventual defeat in the Pacific. In Europe, the conflict was much more concentrated on land; however, the German Navy prioritized the production of submarines, which it used to great effect when attacking transatlantic shipping that supplied the UK - the Battle of the Atlantic would largely be settled by the end of 1943, with the Royal Navy and Commonwealth forces sinking over half of all German U-boats.