Triton

Triton is a Colonial battlestar, destroyed during the Cylon Holocausts in both series. It is named after one of the Lords of Kobol.

The Re-imagined Series

Battlestar Triton, featuring integrated command and control systems, and featuring Dr. Gaius Baltar's Command Navigation Program (CNP) is reported as lost with many other battlestars of the Colonial Fleet during the Cylon Attack, along with the Columbia and Solaria (Miniseries).

The Original Series

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5 Battlestars at Cimtar (credit: Universal / ABC)

Though not specifically seen on screen, the battlestar Triton is mentioned when the Cylons attack the fleet at Cimtar (Saga of a Star World).

It's likely Acropolis and Pacifica are the other unnamed battlestars seen with the Atlantia and Galactica at Cimtar.

Re-imagined Series definition: operating system on military and civilian ships exploited by the Cylons (TRS: "Miniseries, Night 1")