Soldier
The solider unit is the basic ground force for the human GDF resistance. Using a combination of basic ground attacks, soldiers are an integral part of a successful team. Assault Rifles are great for one-on-one duels, while the Rocket Launcher contains the ability to lock-on to enemy vehicles, making the soldier a definite threat against a sloppy ground attack. The HE Charge explosives are used for detonating enemy buildings, and act as the primary soldier objective. No other ally can use HE Charges, so a strong base of soldiers is a must.

Covert Operations
As a hybrid of sniper, soldier, and builder, covert ops can be used to build stations for spawn-point surveillance, as well as in-direct battle using the sniper rifle and scoped assault rifle. At the same time, a perfectly outfitted covert ops soldier can work in tandem up close with soldiers, field ops, and medics if an all-out offensive press is needed. Grabbing the silenced machine-pistol as their primary weapon, covert ops can then participate in building infiltration. Third-eye cameras work great for on-the-fly surveillance and can even be used as a bomb when discovered.

Engineer
On the home front, engineers have the ability to work as builders for the main base, deploying defense turrets for ground, vehicle, and missiles. In addition to the building tools, engineers are often used to infiltrate and sabotage enemy buildings and vehicles. The ability to place mines is also key to strong home defenses. Successful engineers will spend their time securing spawn points by deploying turrets and defaulting to close-range combat with either their shotgun or modified assault rifle/grenade launcher.

Field Ops
As the offensive compliment to the engineer, field ops will be used to build attacking turrets from any human-secured point. Using the three levels of artillery (basic, rocket, and hammer) the field ops is an integral part of the offensive ground-game.

Once turrets are build, field ops are well-suited for vehicle use until up close, in which case they can work as aids for the soldiers or covering units for medics.

Medic
When teammates go down, there's no quick way back into battle. Unless, however, there's a medic around. Using a defibrillator for recovering downed allies, medics can assure that a team stays together and lethal no matter how much opposition there may be. Resurrection is near-instantaneous, and is a definite must-have class on the field. The health pack item can be thrown on the ground for indirect support, and medics can even use the packs on themselves. Say what you will about the importance of any other class, but there's no denying the influence medics can have during a serious online match.