Fourth Armor

The Force Armor, sometimes called the Fourth Armor, is an all-around armor found first in Mega Man X4. In its debut game, it was collected in four parts and slowly got more powerful as the parts were collected, as in the first three games.

Helmet Part, in Cyber Peacock's stage: If you complete the third section in the first part of the level fast enough to recieve an S rating, the Helmet Capsule will be your reward.
 * Increases X's special weapons capacity, allowing him to fire endless uncharged special weapons and use less energy when firing charged weapons.

Body Part, in Magma Dragoon's stage: Found in a passage above and to the right of where the Ride Armor is found. It is reached by dash-jumping in the ride armor from the highest point and ejecting from it in mid-air. Enter the passage to find the Body Capsule.
 * Allows X to use a Giga Attack, the Nova Strike. It is a rushing, invincible, damage-inducing attack, with limited energy that is restored over time. X's damage taken is also cut in half.

Arm Part, in Storm Owl's stage: In the second part of the stage, right before the laser-based miniboss, you may notice a spike-lined vertical passage. To reach the top, fire the Lightning Web right in front of one of the spiky walls and use it to ascend the passage. At the top, you may choose one of two capsules:
 * Capsule 1: Allows X to charge up four charged shots at once. Four icons of plasma will appear next to X's life gauge that are used to keep track of the number of X's shots. Whenever X fires while an icon is visible, he will fire a charged shot.
 * Capsule 2: Upgrades X's charged shots to the Plasma Shot. This shot is much larger and more powerful than the standard blast, and will leave damaging orbs in its wake whenever it comes into contact with an enemy.

Leg Part, in Web Spider's stage: Keep to the right throughout the beginning of the stage. You'll find a break in the wall, and the Leg Capsule will be within it.
 * X can air-dash, and he can also hover by double-jumping. He can move while hovering, but not much.

The Force Armor can also be obtained in Mega Man X5. If X is chosen at the Character Select screen at the beginning, he will begin the game with the Force Armor. The second Arm Capsule is chosen, enabling the Plasma Shot, but the effects of the Helmet Part are not in effect for the duration of the game. The Nova Strike is also unavailable. If Zero is chosen instead, the Force Armor will become damaged in the first stage and be unuseable for the remainder of the game.

Trivia

 * The Force Armor's second name, the "Fourth Armor", is commonly mistaken to be a take on the armor's debut game, Mega Man X4.
 * Since the Ultimate Armor is the most recurring armor in the series (and the fact that it is essentially an upgrade to the Force Armor), most of the Force Armor's abilities (Plasma Shot, Nova Strike and Hover) were also the most recurring abilities in the series.