I've been thinking about a steampunk style world where a lot of the transport is done with balloon powered airships. Obviously there are conflicts and I'm trying to think of ways these craft could be a little more resilient to attack. A flying navy.

At the moment I can't see any reason why a cannon ball through the balloon and the ship will crash fairly spectacularly!

What defensive measures can an airship take to prevent itself from crashing as soon as it's attacked?