Came here to talk about this.
Prince Hamet was the heir to the Tripolitan throne before being usurped by his brother and moving to Egypt to live in exile. The U.S. Marines were sent ashore to assist Prince Hamet in retaking Tripoli from his brother (who had been raiding U.S. ships in the Mediterranean). After the first Combined Joint operation in U.S. Marine history resulted in a complete victory at Derne, Prince Hamet gifted Lieutenant Presley O'Bannon with a Mameluke sword - a scimitar he had presumably obtained in Egypt.
Subsequent to his devastating loss at Derne, of course, the Tripolitan usurper Bashaw Yusef agreed to release the members of the U.S.S. Philadelphia and cease his attacks on Americans on the condition that the Marines withdraw from Derne. So it was that the U.S. political class started its long tradition of abandoning its allies and agreements across the Islamic world...
Today, the Marines honor O'Bannon (one of the barracks at The Basic School in Quantico, Virginia is named after him) and wear a replica of the Mameluke sword in some configurations of our Dress Blue uniform.