Fearless Units containing one or more models with the Fearless special rule automatically pass Pinning, Fear, Regroup tests and Morale checks, but cannot Go to Ground and cannot choose to fail a Morale check due to the Our Weapons Are Useless rule. If a unit has Gone to Ground and then gains the Fearless special rule, all the effects of Go to Ground are immediately cancelled.
Mission Tactics The Mission Tactics special rule represents the unique way in which the Deathwatch go to war. At the start of your first turn, pick one of the Mission Tactics. It will remain active for the entire battle unless you decide to change it as described below. As long as the Tactic is active, it affects all units in your army that have the Mission Tactics special rule.
Once during the battle, at the start of any turn after the first, you can choose to change the current Mission Tactic to another one. 