You should walk up to a group of Marines and call them “ sailors”.
< sigh >
I’m talking about the 1790s and early 1800s. The present-day idea of the Marine Corps as its own separate (almost) co-equal “branch of service” is largely the product of WWI.
Again, the Barbary Wars are well worth knowing about; they are the reason the United States Navy was created; the Marine Corps’ contribution to them (memorialized in that famous phrase from their hymn) was a relatively small part of a much larger operation. That phrase has, however, become the most famous reminder that we’ve been kicking mohammedan tuchus from nearly the beginning of our existence as a nation.