The United States Navy (USN) is the branch of the United States armed forces responsible for conducting naval operations. Its stated mission is "to maintain, train and equip combat-ready Naval forces capable of winning wars, deterring aggression and maintaining freedom of the seas." The U.S. Navy currently numbers nearly 500,000 men and women on active duty or in the Naval Reserve and operates 281 ships and more than 4,000 aircraft.

The United States Navy traces its origins to the Continental Navy, which was established during the American Revolutionary War and was disbanded not long afterwards in 1790. The 1789 ratification of the United States Constitution, however, supported the existence of a standing navy by giving Congress the right "to provide and maintain a navy." Following conflict with Barbary Coast corsairs, Congress enacted this right in 1794 and established a permanent navy by ordering the construction and manning of six frigates. The U.S. Navy came into international prominence in the 20th century, especially during World War II. It was a part of the conflict from the onset of American involvement to the very end of the war and was a vital element in the success of the Allies. The U.S. Navy was involved in the subsequent Cold War, in which it deployed in defense of the United States and its allies primarily as a crisis response force.

The United States Navy still maintains its presence in the world, playing roles in Iraq and elsewhere. Its ability to project force is considered a key asset for the U.S. military. Despite decreases in budget size and the numbers of ships and personnel following the Cold War, the U.S. Navy has continued to spend more on technology development than any other and remains the world’s largest navy with a tonnage greater than that of the next 17 largest combined.

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