The following section contains information from a previous version of StarCraft II which is no longer valid.
In early builds, the tech lab researched upgrades and special abilities for some units, but these upgrades were transferred to the merc compound, armory and fusion core. Currently the tech lab is responsible to research armor and weapon upgrades for the units.
The tech lab was mocked up as a science facility add-on but later repurposed when Blizzard decided that buildings didn't get specific add-ons, rather they could either get a reactor or tech lab.
StarCraft II beta patch 2 decreased the tech lab's build time from 30 seconds to 25, and Patch 6 decreased the cost from 50 minerals and gas to 50 minerals and 25 gas.
In earlier builds the viking was built at the factory in ground mode, but needed the Fighter Tech upgrade to enable it to transform to air mode. In Heart of the Swarm, Siege Tech and 250mm Cannons were removed from the tech lab. In Legacy of the Void, Transformation Servos were removed, and with Patch 3.8 Mag-Field Accelerators was removed, and in the next balance patch its replacement Mag-Field Launchers were also removed.
During development of Legacy of the Void, the tech lab was used to research an upgrade for cyclones that allowed them to gain the ability to attack air units. This upgrade required the presence of the fusion core.
Patch 4.0 added the Smart Servos upgrade, reducing the transformation times of the hellion, hellbat, thor, and viking. The change was chosen to "get more micro" out of terran transformation mechanics.
The thor attacks an enemy ground unit or structure using the cannons on its back. The target unit is stunned for the duration and takes 500 damage. The thor cannot move or attack when using the ability.
"Allows the TF-620 Nomad to use the Defensive Matrix Field ability. Defensive Matrix Field creates a damage suppression field at target location which reduces all incoming damage by 50%."
The Nomad was replaced by the Raven; it had the "Defense Matrix" ability along with another unknown ability at BlizzCon 2007. The ability is no longer in the game.
In December 2012, the ability to research Seeker Missiles for the Raven was removed; the ability is now an automatic one for the Raven. In Legacy of the Void, Caduceus Reactor and Durable Materials were removed, and with Patch 3.8 Explosive Shrapnel Shells was also removed.
Caduceus Reactor would have reduced healing cost. The enhanced healing beam will change color. A fusion core is required for the upgrade. The upgrade was later reverted to the Wings of Liberty version via the January 9, 2013 balance update.
Missile comes out and stays immobile in front of the Raven for 4 seconds while charging up, then rapidly moves (it’s not dodgeable at this point) and explodes at the target, causing 100 damage to target plus splash damage. Targeted unit lights up red when targeted. If the unit moves 13 range out of where the Seeker Missile is, the missile fizzles.
The missile cannot target buildings.
14 (increased to 20 with Durable Materials upgrade) (WoL)
Deploys into Defender mode. In this mode, liberators have a long-ranged narrow attack that can inflict high single target damage. Bonus vision is gained in this mode. Liberators cannot move in this mode.
This attack only targets units, not buildings.