The Battle of Derna at Derna, Cyrenaica, was a military engagement 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, diplomatic Consul to Tripoli, and U.S. Marine Corps First Lieutenant Presley O'Bannon. The battle involved a 521-mile (839-km) march through the Libyan Desert from Alexandria, Egypt, to the eastern port city of Derna, which was defended by a much larger force.