Toy Soldiers

On the level where the Zeppelin appears place a machine gunners, mortars,and tons of barbed wire in the smaller locations for normal enemy protection.

Then fill the larger locations with anti-air, fully upgrade them and the watch it explode and the achievement unlock!

*When I say locations, I mean the spots where you can actually spawn defenses*

Actually, this is probably the easiest of the three boss fights!

All that's needed is two level three anti-air emplacements. It'll take out the Zeppelin by the time it makes a half circuit once around the board. Recommended placement is, facing the entrance to the toy box, directly across from the toy box, and the emplacement directly to the left. Don't even really have to get in a plane to help, unless the rest of the battle is going well, and you just feel like it. This also leaves the other emplacements open for howitzers, with the best coverage arcs over the most number of waves.

It can be done with one level three anti-aircraft emplacement, but it takes a good bit longer, and really necessitates needing to get into the bomber to make sure the planes that appear don't cause too much damage, and sneak into the toy box while the flak cannon is busy.

It's also - if you have secured your ground defences enough to spend some time in the air - entertaining to take the Zeppelin on one-on-one, either with the Camel or the Vimy. Climbing to as high as possible and loosing your bombs on it will hasten its departure nicely.

I managed to easily destroy the Zeplin, by waiting for it to enter the battlefield, then flying over it from behind, go slow and drop bombs on it. Use the bigger plane which reloads bombs.

He'll be gone in no time!