Back in the late 50s or early 60s, an AF 4-star (wish I could remember his name) was asked if the U.S. would ever have a unified military, like Canada does. His reply was, “Yes, it will be called the U.S. Navy.”
I've always found it fascinating that in many sci-fi/near future books there's the Navy and the Marines. Nothing else, so I thought that comment you posted is actually pretty forward thinking! I could see all operations, i.e., space, sea, air, and ground being run by one branch with the Marines to do the dirty work.