Walter is in charge of the Bomb disposal team. You have to guide him around the screen using the Arrow keys and then press the <space> bar to detonate the bombs. BEWARE -- after the fuse has been started, Walter only has 1.5 seconds to move out of the way before the bomb explodes, so you need to be quick!!  To move a bomb along rails, hit the <space> bar twice quickly, then the direction you want to move in.