The United States Navy (USN) is the maritime service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the world's most powerful navy and the largest by tonnage, at 4.5 million tons in 2021 and in 2009 an estimated battle fleet tonnage that exceeded the next 13 navies combined. It has the world's largest aircraft carrier fleet, with 11 in service, 1 undergoing trials, two new carriers under construction, and six other carriers planned as of 2024. With 336,978 personnel on active duty and 101,583 in the Ready Reserve, the U.S. Navy is the third largest of the United States military service branches in terms of personnel. It has 299 deployable combat vessels and about 4,012 operational aircraft as of July 18, 2023.

The Union blockade in the American Civil War was a naval strategy by the United States to prevent the Confederacy from trading.