<P> The history of the United States Navy divides into two major periods: the "Old Navy", a small but respected force of sailing ships that was also notable for innovation in the use of ironclads during the American Civil War, and the "New Navy", the result of a modernization effort that began in the 1880s and made it the largest in the world by the 1920s . </P> <P> The United States Navy claims 13 October 1775 as the date of its official establishment, when the Second Continental Congress passed a resolution creating the Continental Navy . With the end of the American Revolutionary War, the Continental Navy was disbanded . Under first President George Washington threats to American merchant shipping by Barbary pirates from four North African Muslim States, in the Mediterranean, led to the Naval Act of 1794, which created a permanent standing U.S. Navy . The original six frigates were authorized as part of the Act . Over the next 20 years, the Navy fought the French Republic Navy in the Quasi-War (1798--99), Barbary states in the First and Second Barbary Wars, and the British in the War of 1812 . After the War of 1812, the U.S. Navy was at peace until the Mexican--American War in 1846, and served to combat piracy in the Mediterranean and Caribbean seas, as well fighting the slave trade off the coast of West Africa . In 1845, the Naval Academy was founded at old Fort Severn at Annapolis, Maryland by the Chesapeake Bay . In 1861, the American Civil War began and the U.S. Navy fought the small Confederate States Navy with both sailing ships and new revolutionary ironclad ships while forming a blockade that shut down the Confederacy's civilian coastal shipping . After the Civil War, most of its ships were laid up in reserve, and by 1878, the Navy was just 6,000 men . </P>

When did the us navy became the biggest