Only infantry have to take Morale checks – tanks, Dreadnoughts and other vehicles never have to. Particularly monstrous or fanatical units may be immune to the effects of morale, but where this is the case any special rules are included in their description. Note that some units automatically pass Morale checks, while others automatically pass all Leadership tests. This is a subtle but important difference. For example, units immune to Morale checks will still have to test for barrage pinning.
Infantry units normally check Morale in three situations:
A) If they take 25% or more casualties in the shooting phase. Test at the end of the phase.
B) If defeated in close combat in the assault phase. Test once combat results are established.
C) If a tank breaks through their line. Test once the vehicle has moved.