Easy to control units. All infantry can capture buildings, man defenses and swim temporarily but fragile so any bazooka rocket, bomb, shell etc. can do serious damage to them. All infantry can man MG nests, AA Towers, RPG Towers and any defense they found. If the tower is destroyed so does the infantry unit inside it. Also note that any unit of this type can be killed in one hit from a Battlestation.
Grunt
Good in numbers, perfect for infantry, great for capturing structures and weak against tanks.
In nearly all of the missions these units are used as friendly and an enemy unit.
To capture buildings or just jump, shake 
.
Warning! Grunts are used more often rather using Assault Vets.
Bazooka Vets
These Bazooka Vets make light work of vehicles! But their shells are slow moving and easily dodged by infantry
—A-Qira
Elite troopers meant for tanks, any enemy defense tower and most ground foes. Uncharged shots are easily dodged by all infantry.
Hold down 
for a charged shot. Charge shots do more damage and has longer range.
Introduced as a single enemy where the Solar Empire must protect the AA vehicle from a single Bazooka Vet but later fought as a common foe.
Anti Air Vet
These Sharpshooters are trained to bring down enemy air units!
—Herman
Elite anti air troops that can down all aircraft in seconds but ineffective against ground foes.
Introduce because AA Vehicles are quite bulky at small spaces and Frigates are AA only at the sea.
Even for good anti air unit the unit can be easily be killed by Gunships and Bombers if used improperly.
Also hold down to launch a salvo of Rockets. The more charged the shot is the more missiles the gun fires.
Flame Vets
I say! Who is that on the beach? Flame Veterans Advance!
—Colonel Windsor
Soldiers that are very effective against infantry even if they are behind sandbags.
They have to get close to a target to harm them and expect them to be used more often instead of assault vets.
Hold down to keep on continuous burning.
Expect Tanks to be effective against them along with aircraft.
Assault Vets
Elite Assault Veterans advance! Smash the enemy!
—QaLen
Elite Troopers that are ideal against light vehicles and infantry.
Empress Qa-Len points out these Vets are elite troopers.
Hold down for Rapid fire attacking with the Assault Rifle but don’t let the guns overheat.
First introduced in Mission 3 but later fought more often and finally Grunts are used more often than these troopers.
Do not let them attack Tanks nor gunships!
Mortar Vet
Mortar Vets come in handy when attacking foes in trenched positions
—Herman
Good for attacking light vehicles and infantry in cover.
Lord Ferrok claims these troopers were his personal honor vanguards.
Introduced in the Flashback campaign by Herman where these troops are used for sandbags.
Same as Bazooka Vet. Hold down to do a charge shot and do more damage. The more charged the shot is the more range and damage the shot does.
Not used very often due to tanks can just crush the enemy infantry or flame vets get up close and cook them.
Munitions Expert
Set those charges Munitions expert!
—A-Qira
In some missions expect these troopers to be protected because these guys set bombs on things.
Cleanup Soldier
Now escort the cleanup Squad to Windsors Column! They will have Windsor Column scrubbed up in a jiffy!
—Windsor
Colonel Windsor uses these troopers to cleanup messes. Same as Grunts only with cleaning tools. Needs protection a lot.
Staff Bearer
The Staff Bearer has fallen and the strike Battalion along with him!
—Qa-Len
The strongest trooper and this trooper is only playable in the prologue mission. This unit carries a magical staff that provides a shield and supercharges his rifle. Same as a Grunt only with a staff. Weapon is same as Assault Vets (Hold to rapid fire powerful bursts of plasma) only the gun can destroy anything even Battlestations and Gunships.