considering a potential that the future soldier looks a lot like a collegiate. war today is already somewhat academic especially for weapons operation and technical tasks such as air defense.
maybe the union army soldier or union marine corps rank and file of lancer looks totally out of place to our conceptions of a grunt/leatherneck.
Portrait of a Grunt, circa 5016u:
Union. Your ODF bootborne nearly needs a doctorate in the Utopian Pillars before they get their hands on a standard ballistic rifle. Gone are days of the "warrior" mindset: a soldier of the Union is envisioned as a kind of skilled trade-worker. Some people are expert electricians, or plumbers, or HVAC technicians, or arborists or tailors or cooks or what-have-you. A soldier is much the same, with their field of expertise happening to be use of deadly force. They have grenades instead of screwdrivers, rifles instead of saws: it's just another job in service to the Union. Bloodlessly professional in a bloody profession.
SSC. SSC does not have grunts; they have class, a little thing which you may not have heard of. Said class still has its low-rank enforcers, but even their mooks are six-foot-something sports-wear models who can give envy for genders you didn't know existed (but are available on a one-time discount from SSC this season) at sixty paces. Their guns are each personally contoured to fit against their gracefully sculpted cheekbones and nobody else's. Every anti-armor missile's warhead is hand-carved in a charming rococo-revival motif. They don't need mission briefings for the same reason spiders don't need lessons on web-spinning.
IPS-Northstar. Their grunts are the eternal dogface footsloggers, with the exception that these guys throw so many orbital strike beacons you'd think they were reenacting Malevelon Creek. It actually rather gets on their nerves that they really exist to fill in the accuracy margins on shipboard weaponry, so if you're facing them without a barrage barge in orbit, look out, as all that buildup of frustration can make them real mean. (The IPS-N space marines are a whole other branch and ought to be taken much more seriously.)
Harrison Armory. It often goes like this: some young idiot just old enough to legally enlist but not old enough to think they can die goes to one of the famous recruitment raves, a rare break from the usual starched-stiff Armory everyday. Power metal moshpit, hundred-meter barbed wire crawl or full-weight combat pack run or that thing where they get fifty of these adrenaline-drunk teens to do a tug-of-war against one Saladin, all with a Legion gunny screaming at them over the music, they're sweaty, they're hyped, they wanna fistfight the world, and before you know it, they've signed the papers.
HORUS. Rather a mixed bag, as is typical of them. Sometimes it's the lowest circle of initiates to a faith passed backward in time from child to parent since generations vanishing over the horizon of eternity. Sometimes, someone simply wakes up with a wistful smile, a cybernetic tiara sprouting from their brow, and a consuming curiosity as to how much force it takes to bite through somebody's neck and into their jugular, and just finds their way into the ranks from there. Never assume anything: if even the pettiest-looking no-ranker among HORUS grunts says they're a wizard, believe it.