Although they would be expensive, what about massive warheads mounted to relatively crude rockets/liquid metal engines (I think that's the name we agreed upon), which are then launched at airship formations?
What about cannons that launch long, sharp strings of wire at the gas bags of airships? Once they hit something, they wrap around it, lacerating it. In fact, they could be repurposed as trench protection systems, cutting bloody swathes through enemies advancing in no man's land.
Rockets that launch into the air, their warheads spinning rapidly once the rocket reaches a certain distance (how it "knows" it is at the correct distance is a different story). This flings bomblets away from it - they have different loadouts. For example, there are chemical warfare, anti-personnel, high explosive, and incendiary types. They would act as either anti-trench systems or area denial weapons.
Perhaps in the twilight years of the war, they experiment with fitting these liquid metal engines on ground vehicles - same with biplanes and that sort of thing.
I'm terribly sorry, but the air war is my forte, and this is only compounded by my lack of knowledge of the time period.
edited 26th Sep '10 10:40:36 AM by Flanker66