Battle of Vorkado

From Memory Alpha, the free Star Trek reference.

The Battle of Vorkado was a military conflict fought by the Romulans. During the battle, a Romulan captain devised a battle tactic that involved disabling two ships with a photonic shockwave.

Knowledge of this battle, and the tactics used in it, were part of the Emergency Command Hologram's tactical database. (VOY: "Workforce, Part II")

Both the timeframe of the event and the adversary are unknown. However, due to Starfleet's extensive knowledge of the event involving a sworn enemy, it is plausible that the battle was waged against the Federation or one of its allies.