Mechanized walkers (Tiberium)

The concept of an all terrain battle walker, capable of delivering heavy firepower from any location on the battlefield, first surfaced during the period of time between the First Tiberium War and Second Tiberium War in the form of the prototypical bipedal X-O Powersuit. This versatile unit was lightly armoured, but could carry several different weapon systems, which included a 35mm rocket launcher and a high-powered laser. The results of initial tests were so promising, the technology was extensively researched and developed.

GDI walkers
Walkers formed the backbone of the GDI military in the Second Tiberium War, following aforementioned research and development. The Humvee was superseded by a Wolverine Powered Assault Armour with twin autocannons on its arms with recon as its role. The Medium Tank was replaced with the Titan Mk. I Medium Battle Mechanized Walker with a 120mm side-mounted cannon. The Titan had a fairly long range and was often used to take out Nod defenses beyond their range. However, the technology was still being further developed, as the mighty Mammoth Mk. II was being developed.

Following the events of the Second Tiberium War, GDI was expanding on the concept; developing another walker unit, the Juggernaut, equipped with three 120mm naval cannons, as a response to the lack of long range fire support during the Second Tiberium War. CABAL also invented the Cyborg Reaper, which grayed the line between cyborgs and walkers, as well as the massive Core Defender.

However, as with everything, walker technology had its drawbacks. The mechanisms utilized by these units were not only expensive to maintain, and complicated to build—they also required constant maintenance and were relatively weak and fragile in the face of enemy fire, as well as being unreliable in the field. Another weakness was their susceptibility to explosives when placed on legs. As such, the frontline walkers, such as the Titan Mk. II and Mammoth Mk. II, were gradually phased out and replaced with cheaper tanks, such as the MBT-6 Predator and Mammoth Mk. III; with only the long-ranged Juggernaut Mk. III (its chassis based on the Titan Mk. II chassis with a new turret and crew pod, upgraded cannons, and a next generation fire control system) remaining in general service in 2047 due to the walker being intended for indirect fire support and are not expected to be on the front lines, the advantages conferred by all-terrain navigation were deemed worthy of the risks. The Titan Mk. II were not used in the Third Tiberium War by the Steel Talons and were mothballed into GDI Warehouses, with some being repurposed for construction service in Blue Zones.

Following the Third Tiberium War, many in the GDI military felt that the Scrin invasion could have been repelled more easily if they had kept their old mechanized walkers. It was not until the Tiberium Control Network was being constructed that more resilient and maneuverable walker technology was developed. and many walker units were reintroduced alongside their more conventional counterparts. By the Fourth Tiberium War, walkers like the Crawler and the Mastodon were widely deployed.

Nod walkers
Ironically, Nod managed to overcome many of these drawbacks that GDI encountered. First, Nod's Mobile Construction Vehicle became a quadrupedal walker, allowing it to navigate the rugged yellow zones easily. Also, the Black Hand, under Marcion, developed the Purifier walker, equipped with an Obelisk-derived laser, as well as flame weaponry and a subliminal influencing device.

Following the resolution of faction strife, the Purifier was succeeded in general Nod use by the upgradeable Avatar Warmech. The Avatar packed a considerable amount of firepower in its scaled-down Obelisk laser and was sufficiently armoured to take on a large number of smaller ground units. However, it suffered from being costly and vulnerable to attacks from aircraft, but compensated it to a degree with its upgrade capability (in hindsight, this technology was viewed as a drawback of the original design, as many Avatar pilots would deplete their own forces in order to increase their chance of survival). A walker that combines the Avatar technology with GDI's Mammoth Armored Reclamation Vehicle project, the Nod Redeemer is a massive four legged walker armed with a triple-barreled Superlaser and a Rage Generator.

In the Ascension Conflict, the Brotherhood and the Separatists still used walkers, such as the Avatar Mark II Warmech and a new walker from the Crawler family, known as the Offense-class Crawler.

Scrin walkers
When the Scrin invaded Earth, they brought their own mechanized battle walkers with them. However, the technology behind Scrin walkers may be considered far removed from traditional human walker technology, involving bio-mechanical constructs that blur the line between machine and creature.

This created difficulty in what Scrin units could be classified as walkers. Most experts reject the idea of any Scrin "infantry" as being walkers as the workings of their legs are achieved utilizing organic components.

Though Gun Walkers, Shard Walkers and Corrupters are classified as walkers, Annihilator Tripods, Reaper Tripods, and the dreaded Eradicator Hexapod fit the definition in the most traditional sense.