Welcome to Librarium Online!
I'm new to the game and an idiot.
If, for example, you have a squad of 5 marines, 4 with bolters and one with a missle launcher, and you have a leman russ and 10 guardsmen in range, can you have the bolter-marines attack the guardsmen and the missle-guy shoot the tank? Or not?
the entire unit has to fire at a single target