Zack Snyder’s 2011 movie Sucker Punch is a bit of a mess (read our review here), but it has a very cool steampunk World War I scene in it, full of biplanes, zeppelins and undead German soldiers. You can watch parts of it on YouTube.
Jerad S. Marantz was one of the concept artists who helped design the German soldiers. More at his blog.
The Aaron Sims Company provided artwork for the same scene. Here you can see the airships hovering over the trenches. More at Concept Art World.