Romulan patrol ship

From Memory Alpha, the free Star Trek reference

Romulan patrol ships were a type of patrol ship utilized by the Romulan Empire during the mid-24th century.

In 2346, several Romulan patrol ships attacked Khitomer. After receiving a defense access code from from the outpost, the ships were able to lower the outpost's shields, and destroying the outpost.

Twenty years later, one of these ships was captured, and contained the logs that provided new information to the Klingon High Command on the Khitomer attack. The logs, according to Data, "clearly indicate a transmission from the outpost to the Romulans moments before the shields dropped."

The High Command, had learned of the treachery, but according to K'mpec, "only the council knew whose security code had been transmitted. Ja'rod, father of Duras."

Since the House of Duras was powerful, according to K'mpec, "if the truth were known, it would shatter the council, almost certainly plunge us into civil war." Because "someone had to be blamed," the Council revealed that Mogh was responsible for the treason, and since Worf was in Starfleet, they "did not expect [him] to challenge the judgment." (TNG: "Sins of the Father")