Ahh Space Marines. It just makes sense, right? All the landing style operations, close quarters ship-to-ship combat, and generally being a smallish force of highly trained day-ruiners. Except... space combat involves a lot of shiny new gear, which, if the US military is any indication of, flows to everyone but the Marines first.
When you step back from established tropes, it raises a few questions. Who takes charge of space combat ships? Does the Air Force get to call dibs because we've already got a few planes that go right at the edge of space already? Or does the long term nature of space ships get them treated like the capital ships of the Navy? Do we establish an entirely new branch of the military for handling space operations (USSF= United States Space Force?).
For worldbuilding purposes, let's look at a transitional spacefaring culture. The concept of fighting in space is new and untested, but the technology and potential need to do so exist.
Let's imagine that the United States Interstellar Combat Initiative goes through, and calls for the creation of a space combat force using elements of the current military forces.
Air Force: Specialized starport based spacecraft. Interstellar bombers, near-orbit fighters, their craft tend to be purpose built for one or two jobs, and designed for short stints. Very fast, relatively lightly armored, they're meant to go from spaceport to spaceport, or spaceport to target and back to spaceport.
Navy: The big guns and cargo boats. These are the starships, space battlecruisers and interstellar carriers, the landing craft and minesweepers. Life on board is pretty much the same for the crew as it ever was, but with a substantial drop in strolling around on the deck without a full face helmet.
Marines: Exactly what it says on the tin. Space Marines. They still probably wind up with less fancy gear than everybody else, but they make do with grit and training. Drop pods and dropships will probably be their calling cards. A few light vehicles and good old fashioned guns aplenty will do the job.
Army: The sledgehammer of the Interstellar Combat Force. These are the guys you want to dig in and build a base, then fill that base with more planetary defenses than you can shake a spacefleet at. Even with space combat a thing, the old fashioned ground war is unlikely to go the way of the buffalo.
All of these forces would likely initially be rolled into a single group, which would gradually expand as either it got reabsorbed into the various branches, or the various branches were rolled into the new USSF, which then split back into the subdivisions.