Geth Prime

Geth Primes are heavy geth platforms that serve as command units on the battlefield. Larger and more powerful than any other geth infantry platform, Primes are equipped with heavy armor and shields, specialized abilities and a variety of deadly weapons.

Mass Effect
Standing twelve feet high and boasting the deadliest arsenal of any geth infantry, a Geth Prime is a terrifying opponent. They are instantly recognizable by their white armor and huge stature. Primes carry a pulse rifle - which can also launch rockets - have six levels of shielding and are incredibly resilient. They also boost nearby geth combat stats; it is this ability that sets them apart from the Geth Juggernaut. Primes have no major weaknesses and are resistant to biotic and tech talents. They are the largest bi-pedal geth unit, towering over the second largest unit, the Geth Juggernaut.

Tactics
The Geth Prime is used as not only a morale booster for other geth in combat, but also as an elite soldier. They are put into action where the geth need extra armor and firepower. Geth Primes have the Combat VI ability which boosts the combat prowess of all nearby geth, resulting in a faster rate of fire, better accuracy and more damage. Consequently it is a good idea to take out Geth Primes first before focusing on smaller geth.

Mass Effect 2
In Mass Effect 2, Geth Primes are armed with light machine guns and combat drones. They are one of the most dangerous synthetic foes in the game, next to the Geth Colossus and YMIR Mechs.

Capabilities
Offensive

Geth Prime do not seek cover and will generally attempt to engage at point-blank range. There is an exception on Haestrom where a Geth Prime will prefer to stay under the cover of the Geth Recon Drones. They are armed with the M-76 Revenant light machine gun, which they fire in long bursts, and they can melee you with it if you get close. They also have the ability to jam your radar, fire siege pulses and deploy Combat Drones.

Defensive

Geth Primes have high shields, armor and health but do not seek cover.

Tactics

 * Disruptor Ammo and Armor Piercing Ammo, if available, are very effective against their shields and armor, respectively (both possess bonus health damage also). Warp Ammo is effective against their armor and health, and the damage is doubled against enemies being affected by biotic powers. Switching squad weapons to those with the greatest penetration power for that particular defense can augment your ability to damage their defenses even further. These can all be important when fighting Primes, as they possess powerful shields and armor. Seeking cover when fighting them would be wise.
 * Geth Primes tend to close in on Shepard and other squad members, walking around any cover while attacking. It is prudent that the group keep their distance when engaging them. If the Prime gets into point-blank range it can launch melee attacks in the same manner as Shepard.
 * Powers that are useful against their defenses include Overload, Warp and Explosive Combat Drone (distraction allowing free shots at them with low risk, and extra damage when the drone is destroyed). Tactical Cloak can be used if the player can seek separate cover from their squadmates to "ping-pong" the Prime back and forth. AI Hacking can also be very useful as the Prime will quickly eradicate lesser geth units in the area while at the same time taking some damage. While the Prime is under the effect of AI Hacking, either open fire on the Prime, possibly taking it out before the duration ends, or kill off as many other geth troops in the meantime, possibly leaving it alone when the duration ends. Or use the time to pull back and find some new cover. The Prime will not use Combat Drone or Morale Boost while under the effects of AI Hacking.
 * As noted above, Geth Primes will jam your radar, and are one of the only enemies in ME2 which do this. An observant player can take advantage of this by interpreting a jammed radar as an early warning that a Prime is nearby, before they've made visual contact.
 * The Geth Prime will always fire off a single shot before unleashing with a long burst from its weapon. Take cover.

Mass Effect 3
The Geth Prime is also an enemy in Mass Effect 3. Geth Primes are command-and-control units that pulverize their enemies with pulse cannons, missile drones, and gun turrets. The Primes have been redesigned to have three "eyes" instead of one, as well as a red color scheme.

Capabilities
Offensive

The Geth Prime is arguably more dangerous than before. It can deploy a Combat Drone and Geth Turret and wields a lethal semi automatic Pulse Cannon that can drop shields in one or two hits. These cannons also briefly stun you (roughly 1 second), so if you get hit once, you will probably take a second hit. It can also swing the Pulse Cannon at close-by enemies.

Defensive

Primes have had an upgrade to their defenses, and are extremely dangerous without upgraded weapons due to their damage resistance. Primes have strong shielding and heavy armour. They are immune to biotic attacks such as Pull and Throw. Their drones and turrets make it difficult to flank them.

Tactics

 * Cover is a necessity. High-damage attacks such as Warp are effective, but they do not lift easily so a biotic combo explosion can be a challenge to set up.
 * A Prime's pulse cannon blast will stun all but a Krogan Battlemaster with Barrier active. If hit by the first of the three volleys, it is VERY likely that the next two will hit. On Silver and Gold, this will usually kill even the most defensive krogan characters outright.
 * It is possible to use sabotage on a Geth Prime, even at full shields and armor. This also converts any combat drone it has deployed, but not deployed turrets. This gains both a temporary, deadly ally while giving the player the opportunity to focus on other enemies or to wear down the Prime itself.
 * While powerful, the Pulse Cannon can't be fired more than three times in a row before needing a brief pause, which is a good time to return fire. Note, however, that summoning a drone or turret resets the counter.
 * Geth Prime are particularly deadly if you allow them to get close, so maintain the fighting distance at medium to long is recommended.
 * Despite being humanoid, Geth Primes, as an armored target, do not receive extra damage from headshots.
 * A Scorpion paired with Disruptor Ammo can work wonders against Geth Prime, both in dealing actual damage and shock, allowing you time to move to a more favorable fighting position.
 * The Prime will try to keep its drone out at all times. Deploying another turret takes slightly lower priority. As Combat Drones are very weak and not something to worry about unless they sneak up on you, constantly destroying them will often leave the Prime vulnerable.
 * On Silver and Gold difficulties, Primes can at times hard be take down alone, try teaming up, this means that not only will the Prime go down quicker but any players who get downed can be revived quickly to re-enter the fight.
 * Geth Primes are extremely large, and thusly, the game engine has issues keeping track of where they are when they go down inclined parts of maps, including ramps and stairs. This can make lining up shots extremely difficult at times. It is advisable to coax them into level playing fields.
 * With Tactical Cloak and the Black Widow, one can easily down a prime in 6 shots, 2 clips, and 1 reload. First cloak, aim for the torso and fire. There is no need to compensate for recoil, as the shots will travel up the body of the Prime. All 3 shots should expire before the damage bonus does and with proper evolution, all 3 shots might even go off before the cloak runs out. Two cloak-damage-boosted shots should bring his shields to 2 bars. The armor however is a bit harder to remove in a single clip; geth Infiltrators Hunter Mode Damage bonuses and those gained from Networked AI are very beneficial.
 * All characters ingame are right-handed by default. Exploit tall cover that is on your left by standing close enough that you can shoot around it and the Prime cannot shoot you, avoiding chancing the oddball cover system which makes you easily shootable if you stick your head out of cover to fire (even when not scoping in). Combine this with a Tactical Cloak and a Black Widow and there are several spots on any map in which one can down a Prime, solo, in under 15 seconds.
 * The Reegar Carbine projects a short-range cone of lightning. A whole clip will greatly reduce a Prime's shields within a few seconds, if it doesn't strip them outright. This lends itself to hit-and-run tactics--one character removes the prime's shields and draws its attention while the others focus fire on it.

Trivia

 * Geth Prime units on the Pinnacle Station subterranean survival mode are equipped with a large, bluish-glowing version of the Pulse Rifle, which functions in the same manner as the normal Pulse Rifle.