Environment tank

The Nestene creature attacks the Third Doctor from its environment tank. (TV: Spearhead from Space)

An environment tank was a container used by the Nestenes to deposit their energy units in. Once all the units were collected, including the essential Swarm Leader, the energy would coalesce and build a body out of plastic for the Nestenes, designed specifically for the planet they were invading. (TV: Spearhead from Space, COMIC: Business as Usual) An environment tank could be fitted with a voice synthesizer, allowing it to communicate with individuals outside of the Consciousness. (AUDIO: Bridgehead)