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Posse Comitatus Act basically rules out any domestic use of the armed forces
Its text only specifies the Army and Air Force. The Navy, its Marine Corps, the Coastguard, Homeland, Prisons Service, FBI, BATF, DEA and Space Force are all federal agencies (edit- not all are technically ‘agencies’) with military or paramilitary capabilities, and aren’t subject to the PCA. They have their own regulations though.
Adhiero-
Yeah, the omission of the Navy/Marine Corps from the act is slightly weird, given that the Marines have the equivalent of a couple of rapidly-deployable infantry divisions; as you note, the Act's provisions are applied to the Navy through regulations. The Coast Guard are a law enforcement organisation as well as a uniformed service, but they're presumably constrained in a similar fashion (and, purely pragmatically, are less likely to have the forces suitable for staging a coup).
Thrustvector
Posse Comitatus Act basically rules out any domestic use of the armed forces anyhow; states would have to request it, and given as how e.g. the Texas challenge was laughed out of court, there's zero basis for that.