Marine
Weapon: 8mm C-14 "Impaler" Guass Rifle

The first line of defense for most Terran Colonies.  The C-14 Impaler Guass Rifle fires 8mm metal spikes at hypersonic speeds.

Firebat
Weapon: Plasma-based Perdition Flame Throwers

Equipped with powerful arm-mounted flame throwers.  Although Firebats have short range, the flame throwers cause damage to any target caught within the stream.

- StimPack

StimPacks can be used to increase a Marine or Firebat firing rate and movement.  There are some side effects when using StimPacks.  Only Marines and Firebats can stim.

Ghost
Weapon: 25mm C-10 Canister Rifle

The Ghost is a specialist.  This means that he is trained for handling objects like nukes.  The Ghost has special abilities that can be very useful.

- Cloak
The Ghost can cloak to hide himself from enemies.  Works well when nuking.

- Lockdown
Lockdown is very useful against mechanical units.  If fired at a mechanical unit, that unit will not be able to move for a period of time.

- Nuclear Strike
The Ghost can use a targeting laser to direct missiles from any friendly silos.

Medic (Brood War)
Weapon: None

Medics are highly skilled healers.  They can even cure infestations caused by the Zerg.

- Heal
Medics can heal any units at an awesome rate.

- Restoration
Medics can cure infestations such as, Ensnare, Parasite, Lockdown, etc.

- Optic Flare
Medics can blind any units making their sight range very poor.  Blind can be cured by Restoration.

Vulture
Weapon: Anti-Personnel Fragmentation Grenades

Mainly used to scout.  Vultures are fast and can lay mines if upgraded.  Although Spider Mines don't have that much HP, they can do major damage.

Goliath
Weapon: Twin 30mm Autocannons
Secondary: Hellfire Anti-Air Missiles

Goliaths are good at taking out enemy air units.  Their missile range can be upgraded at the Machine Shop (Brood War).  Twin Autocannons are used on ground units.  Goliaths are good at defense if they are in groups.

Arclite Siege Tank
Weapon: Twin 80mm Cannons, 120mm Shock Cannon

Siege Tanks are best on ground defense.  They were designed to serve as a final defense security cannon.  Siege Tanks can transform to Siege Mode, which will increase their range and damage.

SCV (Space Construction Vehicle)
Weapon: Fusion Cutters

SCV's were designed to mine minerals, transport Vespene Gas, and to build.  They are also able to repair damaged units or structures.

Dropship
Weapon: None

Dropships are basically transports.  You can transport units to any location with the Dropships.  Some places cant be reached on foot so you'll need Dropships.

CF/A-17 Wraith
Weapon: Gemini Air-to-Air Missiles, 25mm Burst Laser

Most space battles took place between large capitol ships and smaller gunships.  Technicians made a smaller starship that was able to deal with larger ships.  Wraiths can cloak while in battles to have a better advantage.  Wraiths can attack ground and air units.

Behemoth Battlecruiser
Weapon: Laser Batteries, Yamato Cannon (Limited Availability)

Battlecrusiers were designed to keep peace within Terran sectors.  They are also equipped with a very powerful Cannon (Yamato Gun) that can almost blast through any defense.

Explorer Science Vessel
Weapon: None

The Science Vessel can use special abilities to defend and attack units.

- Defensive Matrix
The Science Vessel can create a large force field around any units to protect them from enemy fire.

- EMP Shockwave
If the EMP is fired at a unit or structure with shields or energy, that unit or structure will lose all energy and shields.

- Irradiate
The Science Vessel can create a stream of radioactive particles that can damage certain units and the units nearby.

Valkyrie (Brood War)
Weapon: H.A.L.O. Cluster Rockets

The missiles are fired in volleys of fourteen.  Valkyries can reduce most star fighters to rubble.  Valkyries are heavily armored and can deal with most starships.