Silurian battlecruisers were used by the Silurians and Sea Devils during their reign of the Earth in pre-historic times. They were built using organic material, not metal. They radiate heat that can be detected.
The battlecruisers were the equivalent of human submarines and were designed to dock with the Sea Devil colonies on the sea bed. The battlecruisers were also equipped with a particle suppressor as a defensive weapon and would reflect energy weapons back onto the source. (TV: Warriors of the Deep)
The Third Doctor, Tahni and Marc Marshall stole a battlecruiser when they attempted to escape the Silurian base underneath L'Ithe. Auggi D'jo had the cruiser destroyed, forcing the Doctor, Tahni and Marc to swim to the surface. (PROSE: The Scales of Injustice)
One battlecruiser was that of Silurian Triad member Icthar and his two companions, Scibus and Tarpok. In 2084, Icthar used it to collect the Sea Devils of Elite Group One and then attack and invade Sea Base 4. (TV: Warriors of the Deep)
