The film is a fictionalized account of the Battle of Derna at Derna, a coastal town in modern eastern Libya in April 1805 against Tripoli, one of the four Barbary states in North Africa and stars John Payne, Maureen O'Hara, Howard Da Silva, Phillip Reed, Grant Withers, Lowell Gilmore and Connie Gilchrist.

In 1805, the USS Essex is part of a blockade of the port of Tripoli by the small United States Navy Mediterranean squadron, targeting pirates menacing American shipping.

American diplomatic Consul William Eaton (Herbert Heyes) comes on board to recruit a small commando squad for a secret mission.

Hamet Karamanly (Phillip Reed), exiled former Pasha of Derna, supplies men in exchange for being restored to his throne which was taken by his brother.

O'Bannon recruits a native force of mercenaries - Greeks, Turks and Arabs - to accompany his Marines and some American soldiers and Navy midshipmen.

D’Arneau defies O’Bannon and accompanies the expedition from Alexandria, Egypt, across the North African deserts, but he forces her to travel with the camp followers.