The role of the JCS was revised by the Goldwater - Nichols act of 1986, and created the opportunity for a Marine to ascend to Chairman of the JCS. The Marine Corps gained great independence from that act.
Oorah!!
No, not "part of the Navy", but certainly under "Department of the Navy", hence the attached Corpsmen, etc. - so it's semantics.
Semper Fi! 1966-68