My chief engineer tells me that he's managed to get one of the bombers repaired and airworthy. Take these bombs with you, and look for the repaired bomber at the start of the runway.
Once you're airborne, use the bombs to do as much damage to the attacking Dark Iron dwarves as you can. I've heard rumors that they're preparing to deploy a new kind of war golem. Keep your eyes peeled for those golems and make them your highest priority targets.