What it will do: Your character will get down and slide forward on one knee until they either lose momentum or collide with a wall or something like that. Your character can still fire his weapon, but accuracy will be decreased.
What it is for: Useful for getting into cover quickly while under fire.
Without sliding, you would have to stay fully upright until you reached the cover, exposing you to enemy fire a lot. Or you could crouch down and slowly meander towards the cover, your slow speed making you an easy target to hit until you get into cover. Sliding combines the decreased target area of a crouching character with the speed of one that is upright and sprinting, giving you a sudden burst of speed allowing you to get to safety.
How: My suggested method of executing a slide is: Standing upright, move forwards in the desire direction, then DOUBLE TAP AND HOLD the S key to slide in the current direction. Your character will drop down on one knee and slide forwards until colliding with another object or losing momentum.
Whether or not the AI will be able to do this can be decided by the developer, and there should be an Engine Mark or Trigger Action to disable this as well.
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