A Voice in the Warp
Characters that have been knocked down, or choose to go prone count as being in the prone position. (You count as going prone by default while setting up a weapon with a bipod on open ground) Weapon skill tests against prone targets count as ordinary(+ 10). Weapon skill tests from a prone position are difficult (- 10). Ballistic skill tests for characters in prone suffer no penalty unless they become engaged in hand to hand combat in which case ballistic skill tests become difficult (- 10). Dodge tests in prone count as hard (- 20) if engaged in hand to hand, and count as challenging (+ 0) against ranged attacks. Additionally against ranged attacks you count as one size category smaller if you are prone.
Going prone is a half action