Does the artillery fire at the final battle only happen if you do this quest? Or does it happen regardless?

EDIT: I Hear You Knocking* The quest Lucius gives you to find a new firing mechanism for the howitzer.

I can't recall what it actually does during the final battle when you are playing, but I do know that in the scheme of things, the howizter will help the legion hit those coward profligate rangers hiding behind their walls.

Anyone else?