Librarian

Individual model. Can join other units in battle

Automatically regroup when falling back even when at less than 50%. Enemy advances are treated as a new Assault (enemy striking +1A the following turn). If the enemy does not advance, the Space Marines can move, shoot, and assault as normal in their following turn.

The unit will automatically pass any Morale checks they have to take, even if faced by a situation or opponent that would normally cause them to automatically fail. Note that they still must test for pinning as normal.