This is new? The US Navy OWNS the USMC,and has owned them since Day One. They have been training to work together since Day Two.
To varying degrees, all branches may cooperate. TheWWII Okinawa amphib landing included units of both the Marines, and the Army. Transported by Navy vessels.
Now both Navy and Marines, have planes. Fixed and rotary wing I believe.
I think they assemble the pieces they need, mission by mission.