The United States Marine Corps of Jack’s childhood was actually America’s primary planetary combat arm. They used both Army and Space Force designs to fight on the ground and to secure the planetary orbitals, and they built their own Marine designs when they needed something to fill a niche those didn’t. They worked out of Army or Space Force bases, and deployed with every Naval ship in the cosmos, which allowed them to continue the old tradition that “every Marine is a rifleman.” Or a mech pilot. Or a tank driver. Maybe a fighter pilot. In the end, if you were a kid who wanted to play with guns and go to the stars, you wanted to be a Space Marine. When things were going wrong and the Americans needed to send someone to personally sort the bad guys out, it was usually the Marines who rode in to stack the bodies. Or they caught the smugglers trying to avoid local laws. Maybe they just boarded your broken down spacecraft and brought you back to the Navy starship that had come all this way to rescue you. Or they delivered disaster relief supplies. The Marines did a little bit of everything, and so they could be seen everywhere that America went.