An Engineer can also replace one crew member of a war machine he joins, including Volley Guns (which will fire using the Engineer's Ballistic Skill) and Rocket Batteries, but if the Engineer is operating the machine, he cannot fire his own missile weapon. If a machine with an Engineer attached to it explodes, the Engineer will be killed with the rest of the crew if he replaced a crewman or used his re-roll ability during that turn (ie, if he was too close to the gun when it exploded!).