Torpedo Dalek

The Torpedo Dalek was the underwater version of the Special Weapons Dalek, so named because of the brief and often fatal encounters with them. This type of Dalek was first sighted in the initial battles on the largely ocean-covered planet Guria and was indeed initially mistaken for a submarine torpedo. However, capture and analysis of this type revealed its cunning adaptability.

Equipped with an advanced caterpillar drive, the underwater equivalent of a jet engine, and packed with formidable power reserves, the Torpedo Dalek was more than a match for any military submarine. The ingenuity of its design, however, allowed its outer casing to react with seawater in order to temporarily alter the molecular structure of the bonded polycarbide shell. The nature of the structure was governed by an onboard menu of molecules stored in the Dalek's battle computer, allowing the Torpedo Dalek to assume the appearance, texture, and feel of objects such as a rock on the seabed or a log floating in the water. In situations of dire emergency, the Torpedo Dalek could actually become a torpedo, being preconditioned to sacrifice itself with maximum explosive force should the situation call for it. (PROSE: Dalek Survival Guide)

History
On the planet Steraxius, a flotilla of Torpedo Daleks posed as a shoal of beached water mammals in distress. As the Steraxian Ecological Foundation operatives approached them, the Torpedos opened fire, devastating a large proportion of the planet's defenses and leaving it open to Dalek conquest. The Dalek Survival Guide counted this as the greatest victory achieved by Special Weapons Daleks.

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