The Battle Blimp Siege Machine is an air unit designed to fly over walls directly to the Town Hall. As it flies through the skies it leaves a trail of carnage in its path, dropping bombs on any buildings it crosses over.
If you deploy the troops inside, the Battle Blimp is destroyed. Naturally defenses can also destroy the Battle Blimp, causing the units to be deployed.
Upgrade the Battle Blimp in the Laboratory to increase it's hitpoints as well as the damage it deals.
Workshop level 2 is required to unlock the Battle Blimp.