Tier

Tiers in Command & Conquer refer to the tech level of a base and the technology required to produce a unit or structure. At higher tiers, more advanced and powerful units are available.

There are roughly three tiers of units:


 * Tier 1: All that is required for production is the base production structure (e.g. Construction Yard, Barracks). Includes light vehicles, tanks, and basic infantry.
 * Tier 2: Requires an additional technology structure (e.g. Command Post). Allows more advanced units and structures to be built.
 * Tier 3: Requires an expensive high-tech structure (e.g. Battle Lab). Allows for construction of very advanced units and structures, such as the Obelisk of Light and Mammoth Tanks. Occasionally further requirements may be needed, such as a construction hub for Epic units.

Game overview
Tiberian Dawn=

Tiberian Dawn
Both sides have the Communications Center as their tier 2 structure. GDI has the Advanced Communication Center as it's tier 3 structure while Nod instead has the Temple of Nod.

GDI can build their powerful Mammoth tanks by only requiring the Repair facility.

Nod can build their stealth tanks and most of their advanced units with only a communications center.

Red Alert=

Red Alert
Both sides in Red Alert 1 are uniformed. The second tier is unlocked through the Radar dome, and the third one with the Allied or Soviet tech centers respectively.

The Allies tech center allows the allies to build thief, chrono tanks, the chronosphere, and the cruiser.

The Soviet tech center allows the Soviets to build the mammoth tanks, the flame trooper, the Missile submarine and finally the MAD tank.

Tiberian Sun=

Tiberian Sun
Both GDI and Nod use Radar stations to unlock tier 2 tech and GDI and Nod Tech Centers for tier 3 tech. Some units also required Upgrade center or Temple of Nod.

Red Alert 2=

Red Alert 2
Like in Red Alert 1, all three sides are uniformed in Red Alert 2 and Yuri's Revenge. The second tier is unlocked through a radar-revealing structure: the Airforce Command Headquarters for the Allies, the Radar tower for the Soviets and the Psychic radar for Yuri.

The third tier is unlocked through one of the three Battle labs (Allied, Soviet or Yuri).

Generals=

Generals
There is only one tech structure per faction in Generals, unlike the usual two per faction in other Command & Conquer games.

The USA requires a Strategy Center in order to construct advanced units and structures like the Tomahawk Launcher and Aurora Bomber.

China has the Propaganda Center for construction of advanced units and structures such as the Overlord tank and Nuclear Missile Silo.

The GLA uses the Palace to gain access to advanced units and structures such as Jarmen Kell and the Scud Storm.

Tiberium Wars=

Tiberium Wars
Most artillery require Tier 2 to 3 to be built.

The Command post, Operations center, and Nerve Center serve as the tier 2 structures of GDI, Nod, and Scrin respectively.

For Tier 3 GDI uses a Tech center in order to build advanced units and structures such as the Mammoth Tank and Firehawk. A "Tier 4" structure, the Space Command Uplink, is available for GDI and provides support powers such as Shockwave Artillery.

Nod instead employs a Technology Lab to allow construction of advanced units and structures like the Avatar Warmech and Vertigo Bomber. Nod also has a "Tier 4" structure, the Tiberium Chemical Plant, for support powers such as Seed Tiberium.

The Scrin use Technology Assemblers to build tier 3 units and structures like the Annihilator Tripod and Storm Column. The Scrin's Signal Transmitter, a "Tier 4" structure, is unique in that it is required to build a unit (the Planetary Assault Carrier) and summon another (the Mothership), in addition to providing support powers like Overlord's Wrath.

In addition, Epic units cannot be built straight after a Tier 3 structure. A specialized Tier 3 Epic production structure must be built first, and only then can construction commence.

Red Alert 3=

Red Alert 3
The three factions in Red Alert 3 each have unique mechanisms for access to advanced units and structures. Significantly, basic tanks for all factions in Red Alert 3 require Tier 2 to be built.

Allied structures are linked to the nearest Construction yard or Command Hub. These structures are upgraded to Heightened Clearance and then to Max Clearance, and the structures linked to those buildings gain the ability to produce more advanced units. If this link is lost (through the Construction yard unpacking or being destroyed, or the Command Hub being sold or destroyed), then production structures formerly linked to it will lose it, thus they can only produce basic units. In addition, the Defense Bureau provides further access to extremely advanced units and structures.


 * Regular Clearance allows basic units such as Peacekeeper, Riptide ACVs, and Vindicators to be constructed.
 * Heightened Clearance allows the Guardian Tank, Cryocopter, Assault Destroyer, and Spy to be produced.
 * Max Clearance allows advanced units such as the Mirage Tank to be built.
 * Defense Bureau; an advanced technology center allows structures such as the Spectrum Tower and Proton Collider to be built.
 * Finally, with Clearance and Defense Bureau, the extremely advanced units classified by FutureTech such as the Future Tank X-1, Cryo Legionnaire or Harbinger Gunship are provided to be built

The Empire of the Rising Sun upgrades each of their production structures individually. However, a special building, the Nanotech Mainframe, is required to upgrade any structure to Tier 3. Unlike Allied tier upgrades, tier which production and key structures are independent will be lost upon destruction and each production tier is maximum, it won't affect others productions in game.

e.g. You build 2 Mecha Bays, you need to upgrade breakthrough both 2 bays if you want to build 2 King Onis at the same time. However, if 1 maximum Mecha Bay is destroyed, other Mecha Bays ARE NOT reduce tier to level 1
 * Tier 1 allows basic units such as Imperial Warriors and Mecha Tengus to be built.
 * Tier 2 allows more advanced units such as the Shinobi and Tsunami Tank.
 * Tier 3 allows for construction of advanced units and structure cores like the King Oni and the Psionic Decimator.

The Soviet Union follows the traditional method of constructing certain buildings for technological advancement. A Super Reactor is required to reach Tier 2, and a Battle Lab is required to reach Tier 3. However, unlike their counterparts, if they lose all Super Reactors and they still have at least 1 Battle Lab, they only will lose access to Tier 2 units.


 * Tier 1 allows basic units and structures to be built, for example the Sickle and Sentry Gun.
 * Tier 2 allows more advanced units and structures to be built, like the Airfield, Tesla Coil, Akula Subs, and Hammer Tanks.
 * Tier 3 allows for highly advanced units and structures to be produced, such as Apocalypse Tanks, Kirov airships, Dreadnoughts, and Natasha.

Tiberian Twilight=

Tiberian Twilight
In Tiberian Twilight, the traditional tier system has been replaced in favor of online progression.

First, as Tiberian Twilight is online game and you need to level up to unlock higher tiers. Higher level you have achieved, more technologies you can access.
 * To unlock Tier 2 upgrade, your level must be 5
 * To unlock Tier 3 upgrade, your level must be 12

Both GDI and Nod have many access authorities and you must collect Tiberium Core to use as upgrade point. Tiberium Core appears on both campaign and multiplayer map and upgrade point will be come as you collect the following
 * Green and Blue Tiberium Core will be provided on Tiberium Drop Zone, collecting one and return to MCV drop zone will give 1 upgrade point (2 for Blue Tiberium). Most units, however, can collect only one and it is double edged sword weapon; increase weapon damage in exchange of slow and decrease defensive power, let collector to be destroyed easier. To counter some situations, sometimes collector can choose to Detonate Tiberium Core, suicide oneself and unleash Ion Storm that harm most target including allies and your own for a short time.
 * Red Tiberium Core can be found only campaign, collecting one will not need to return to drop zone but provide the most (5 upgrade points). Be careful, it is valuable but you can play with allies. Manage and share with them is the best way to solve.

Then, you need some upgrade points to unlock Tier Upgrade and the you will now access to call higher tier reinforcement.
 * Tier 2 cost 5 upgrade points, 0.00 time upgrade
 * Tier 3 cost 9 upgrade points, 0.00 time upgrade

As you have lost your MCV, your new one will still persist your technologies tier, even your different classes.

e.g. First you play as Offensive Class and you upgrade up to Tier 2. If your MCV is destroyed, when you call a different one like Support Class, your Support Class will still be Tier 2. Only the change is skill researches and upgrades which you must all newly upgrade.

Strategy
Since tech structures are usually expensive, time-consuming to construct, and poorly-armored, they are a high priority target. Destruction of a tech structure is easy, and can interrupt production of advanced and powerful units or progress to the next Tier, with significant amounts of time and resources required to rebuild the tech structure.