I'm thinking about how in the history of modern military organization, there was a VIOLENT struggle between branches of the U.S. military over what branch of the military would control new and developing frontiers of combat. Basically, new theaters of warfare. This is a highly simplified version of events, so for those of you who may know more about this than me, forgive me for the simplification. And it's from an American perspective.
Sea - In early naval warfare, it was necessary for men of highly specialized maritime talents and training to actually man the vessels. I'm not by any means an expert of naval warfare or its evolution, but I know that in the early days of western civilization, things were done differently by different people. For example, as cited in the modern Marine Corps novel "One Bullet Away" regarding the early lessons on the need for specialized amphibious troops, Julius Caesar suffered great losses when he attempted to invade Britain on multiple occasions. His men were sailors, to be sure, but attempting to dismount their vessels with combat gear and engaging the enemy while wading ashore and fighting the surf proved a task beyond them. From what I understand, it was in the 16th century that the Spanish first specifically trained troops for amphibious operations. These were the first professionally trained Marines.
Air - I know only of American air combat units that early on, it was a highly specialized area of the Army - the Army Air Corps. Later, in one of those many Defense Reorganization Acts of the 1940's and 50's immediately following WW2, the United States Air Force was born. Today, there IS an "Air and Space Command" under the purview of the USAF, but to my (and the public's) knowledge, it is only an information-gathering operation. I would not be surprised if there are crack security forces that guard highly classified defense department launch sites that put spy (and other) satellites into orbit; and as a technical organization, the USAF is responsible for putting defense, spy and ABM related systems into space... It's possible and very probable that they will one day try to claim space as their own theater of infantry combat.
A special note about the Unites States Marine Corps. Naturally


The point of all this is in American military history, and by similar history, every other modern major military, emerging new theaters of warfare, whether they are sea, or air, have engendered fierce and vitriolic struggles for control of the emerging theater. This is primarily because the haste of war usually introduces a new frontier before the involved parties have had time to explore and develop new technologies for tackling it, so usually something haphazard is put into place until specialized troops, facilities, knowledge bases, and equipment can be developed.
The same would likely be true for the emerging environment of space. It certainly qualifies as an environment that demands highly a specialized force. Although I have employed "Starfleet Marines" in my own fics, I concede that there is no reason to assume that a force that was historically responsible for ownership of amphibious landings would necessarily own space combat.
What is your opinion of what kind of force -- MACOs, Marines, starship security, etc -- would end up in control of space as a ground operation? Would it, in fact, be spread between something like starship security and ground forces? In the Navy, Marines have historically taken the responsibility of sentry detachments and ground troops at the same time. Historically, I think this is because they were originally intended to be a force wholly separate from the crew to put down mutinies and protect the officers of the ship. It was later that they would be used as ground forces.
MACOs are presumably like Delta Force or Army Special Forces today. Perhaps DEVGRU or even a CIA SAD (Special Activities Division) is a more appropriate categorization, it depends on just how super elite they were supposed to be. SAD probably doesn't fit at least in culture and organization, as they seemed to have a more conventional rank structure and hierarchy and included many enlistedmen, which SAD does not. Would super elite conventional ground forces get the nod? Would a whole new branch be born?
Just curious what people think.