Gundam X

Serial Number: GX-9900
First Appearance: "Is the Moon Rising?" (episode 1)
Weapons and Armaments: Chest Vulcan, Shoulder Vulcan, Buster Rifle/Shield, Huge Beam Saber, Satellite Cannon
Height: 17.1 m
Weight: 7.5 t
Armor: Luna Titanium Alloy
Pilots: Jamil Neate (15 years old), Garrod Ran

First piloted by former Newtype Jamil Neate during the 7th Space War, Garrod Ran, while escaping with Tifa Adil from her would-be captors, found an abandoned (but still active) GX in a run-down Federation MS production building. How it got there in the first place was not fully explained. Nonetheless, the GX had greatly helped Garrod fight against Ranto's group, the other Vultures, and finally the Frosts brothers as well.

Gundam X Divider

Serial Number: GX-9900-DV
First Appearance: "Just Run Without Thinking!" (episode 11)
Weapons and Armaments: Divider/Harmonica Cannon, Beam Machine Gun, Beam Sword, Chest Vulcan
Height: 17.1 m
Weight: 7.7 t
Armor: Luna Titanium Alloy
Pilots: Garrod Ran, Jamil Neate

When Caris Nautilus and his Vertigo defeated the GX in a one-to-one combat, it's powerful bits had greatly decimated GX's solar panels, rendering the Satellite Cannon useless. Kid Salsmille, the Freeden's chief engineer, eagerly took this opportunity to suggest for an upgrade for the GX, giving it some customized armaments that he had recently created. Jamil Neate, after fully recovering from his cockpit phobia, became the GX Divider's new  pilot a few episodes later after Garrod obtained the Double X.

Gundam Double X

Serial Number: GX-9901-DX
First Appearance: "The Ghost of 15 Years Ago" (episode 22)
Weapons and Armaments: Twin Satellite Cannon, Buster Rifle, Hyper Beam Sword, Chest Launcher, Head Vulcan
Height: 17.0 m
Weight: 7.8 t
Armor: Luna Titanium Alloy
Pilots: Garrod Ran

The new Gundam secretly developed by the New Earth Federation in an obscured island named Zonda Epta. Imzat, the Frosts' rather ambitious superior officer, had used this Gundam to bluff Jamil into surrendering. His  victory was short-lived though, when the Freeden crew not only managed to escape from their prison but Garrod, with the aid of Jamil, Tifa and Kadok, had successfully stolen the DX. It's computer was based from Jamil's own battle data during the war. And unlike GX, Double X can use its Satellite Cannons without restriction.

G-Falcon Unit Double X

Serial Number: NA
First Appearance: "How Do You Know Me?" (episode 33)
Weapons and Armaments: Same weapons equipped by both the DX and the G-Falcon
Height: NA
Weight: 13.9 t
Armor: Luna Titanium Alloy
Pilots: Garrod Ran, Paula Cis (joint unit)

When Garrod left Earth to rescue Tifa, who was taken against her will to the Colonies, he befriended a young girl named Paula Cis after the latter rescued him from Lancerow Darell's group. They became comrades in arms, especially when Paula's fighter plane, the G-Falcon, can combine with the Double X (as well as Airmaster and Leopard).  It was proven time and again (both in the anime series and their game counterparts) that these two would make a force worth reckoning.