Its worth noting all a soldier really needs is the soldier skill and guns (riffle). The soldier skill will let the soldier comprehend doctrine, dig foxholes, and use his radio properly. Guns (riffle) lets him hit targets with his riffle. That's all you really need, particularly for conscripts or privates.
Having said that, its worth pointing you towards the list of
skills every adventurer should have. This isn't meant for soldiers, but it is pretty applicable.
And then you have specialties in the military. Those are probably actually the hard part.
If you have Gurps: Space, its templates translate to modern day folks pretty darn well.
If you're picking up specialists, it will stand alone, and it does a pretty good job. I do have a couple tweaks I like to make in military contexts:
In tactical driving, add "Tracked" to the list of specialties. Remove the perk, shadowing, and urban survival. Add Soldier [2], Tactics [4], and saviore-fairre (military) [1]. This creates a military driver.
I also like to add a "Weapons Crew" package. This is separate from "heavy weapons" because its focused around vehicle mounted weapons, and its a bit more skill based.
Freight Handling IQ/A [1], Tactics (IQ/H) [4], Soldier (IQ/A) [2].
16 points in: Artillery (Bombs, Cannon, guided missile, torpedo), Gunner (Cannon, Machine Gun, Rockets), or Electronics Operation (Electronics Warfare, Sensors)
[2] points in one of Driving (automobile, heavy wheeled, Tracked), Piloting (helicopter, high performance plane, heavy airplane), boating (motor boat), seamanship, or submariner.
Yes, it has a lot of options. But its shaped right!