Ground
Infantry
Most common unit in the game. Weak against everything but other infantry, yet essential because they can capture buildings being the only 2 units to do so.
Mech
A slightly more powerful version of the Infantry unit, but with a smaller movement range and 3 times more expensive. Mech units come equipped with bazookas and are able to effectively neutralise light tanks, recon units, artillery, rockets, and APCs, but only if they strike first. They can also capture buildings.
Recon
A basic vehicular unit. Effective against infantry, mech, and other recon units. This unit though lacking in firepower has a large movement range and sight range, making it an essential part of any campaign, especially in Fog of War situations.
Tank
Field control. Takes on infantry, artillery, rockets, anti air guns, anti-air missiles, and other tanks with effective results. Weak against MD tanks, bombers, helicopters, and naval units. The tank is the weakest, but the cheapest tank you can buy.
Medium Tank
The Medium tank is the most powerful yet most expensivee ground unit in the game. It is effective against almost everything. How ever it is still easy to beat if you have Bombers, any indirect fire units like artillery, rockets, and battleships. Helicopters are also somewhat effective because since they are airborne, the medium tank is forced to use its far less powerful machine gun instead of its main cannon. However the helicopter does an equal amount of damage.
Anti Air Vehicle
Effective in taking down air units and infantry, but weak against tanks.
Artillery
A long range unit that can only fire if it has not moved and 2-3 spaces away from target. Effective against all ground and sea units. It can not fire if an enemy is right next to it so be sure to keep your distance. Best used in chokepoints ir if protected by other units.
Rockets
An upgraded version of the artillery unit that does slightly more damage, but more expensive and less armor. Forces Artillery to move or get hit. Once again use other ground units to protect it.
Missiles
Similar to the rocket unit, except it specializes in taking down air units. Although powerful enough to one-shot all air units, this unit requires major caution as air units move more than the missile's range. It is very good for this task and also has a high range of sight in fog of war. Keep it surrounded by other units.
APC
APCs are a very useful unit. They can transport one infantry or mech unit. Also they are very essential because they can refuel and resupply ammo to any unit directly next to it. This unit has no weapon and cannot attack, but can be used as a decoy to lure enemy units.
Sea
Lander
A sea unit transporter, able to transport infantry or any other ground unit two at a time. Cannot attack, so keep it well protected.
Submarine
Unit with the ability to dive, rendering it invisible to the enemy until it is right next to them. Keep in mind that it runs out of gas quickly, and keep it away from cruisers.
Cruiser
Great units if you have a submarine and air unit problem, but vulnerable to battleships. Can also hold helicopters.
Battleship
Ranged unit that can shoot the farthest out of all units in the game. Can attack sea and ground units, but bad against submarines.
Air
Transport Copter
Transport Copters, AKA T Copters, are an aerial version of APCs. Due to their aerial abilities they are very useful for transporting and rescuing Infantry units. They are however, very vulnerable to aerial attacks. They cannot, however, supply adjacent allied units with ammunition and fuel.
Battle Copter
AKA B Copter. Counters small tanks and other ground units effectively, EXCEPT for Anti-Air Tanks. Avoid engaging with Anti-Airs and Fighters.
Fighter
Air unit who's purpose is one thing: Crushing other air units. It does a good job of it too. Very strong against any air units, just try to get a first attack if the enemy unit is a fighter as well. Do not make if the enemy has no air units.
Bomber
Great for blowing up anything on the ground, even anti air doesn't stand a chance if you get a first attack. Just remember that a fighter can easily knock it out of the sky, so keep it protected.