How many Marines were part of the war party in Tripoli?

The correct answer is seven because during the First Barbary War, specifically in the context of the raid led by Lieutenant Presley O'Bannon in 1805, a small group of Marines played a crucial role in the assault on the city of Derna in Libya. The operation is famously known as the "O'Bannon Raid," where O'Bannon and his contingent of seven Marines, along with a number of local forces, demonstrated the U.S. military's commitment to defeating piracy and securing maritime rights. This event is significant in Marine Corps history, as it marked one of the first times American forces fought overseas and established a legacy that has been honored in various forms ever since, including the Marine Corps hymn referencing "the shores of Tripoli."

The other options do not accurately reflect the historical details of the raid, as the number of Marines involved was specifically seven, making it a distinctive point in U.S. military history.