The Guernik was a Breen privateer warship.
In 2379, Starfleet Special Operations disabled the Guernik in the Ravanar star system. In 2382, Julian Bashir and Sarina Douglas posed as crewmembers of the Guernik, which was destroyed so the Breen would rescue them. Bashir and Douglas left the vessel aboard an escape pod. (ST - Typhon Pact novel: Zero Sum Game)