While in the detachment selection screen, hold down the control key and type Paladin. This enables you to use Knight Paladin units.

During the battle, hold down the control key and type:

EYEOFTERROR : To be able to see all enemy units.
HERETIC : Completes the mission.
CLEANSINGFIRE : Your hit probability is increased to 100%.
WHITEDWARF : Makes all your units invulnerable to ranged weapon fire, not close combat.

P.S Control makes the selected unit fire so try to select a unit that has fired or it cannot fire.