Keladon gull

On Oceanaron, a flotilla of Torpedo Daleks not-so-cunningly disguised themselves as rather large floating mounds of Dalek-shaped Keladon gull dung only to be destroyed as a result of a low-level chemical weapon bombing raid which transformed the planetoid's oceans into highly corrosive acid. The Dalek Survival Guide counted this as the greatest defeat incurred by Special Weapons Daleks. (PROSE: Dalek Survival Guide)