The Battle of Derna at Derna, Cyrenaica is the decisive victory in April–May 1805 of a mercenary army recruited and led by United States Marines under the command of U.S. Army Lieutenant William Eaton, (1764-1811), diplomatic Consul to Tripoli, and U.S. Marine Corps First Lieutenant Presley Neville O’Bannon (1776-1850).

The battle involves a forced five hundred-mile march through the North African desert from Alexandria, Egypt to the eastern port city of Derna, Libya, which wss defended by a much larger force.