The Battle of Okardo 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 the Starfleet's extensive knowledge of the event involving a sworn enemy, it is plausable that the battle was waged against the Federation or one of its' allies, such as the Klingons.