The Hydra is a warship in Red Faction: Guerrilla
Following the Red Faction's destruction of an Earth Defense Force base in Tharsis, The EDF's Admiral Lucius Kobel, Commander of the Fleet, deploys The Hydra, a massive warship (And the most powerful one ever built) towards Mars. Stocked with fearsome weaponry and thousands of hardened reinforcements, the Hydra's mission is to crush the rebellion... even if it means annihilating every man, woman and child on Mars.
During the events of Red Faction: Guerrilla, the Hydra was proclaimed by the Earth Defense Council and indeed the EDF as the largest ship ever built. With the most effective weapons capable of destroying enemies from orbit with particle-beam based weaponry, which posed a massive threat to the Red Faction.
The Red Faction - who eventually allied with the mysterious Marauders - captured the Nano Forge, planning to use it against the Hydra. Using the Nano Forge to disintegrate the Hydra, which by the time they were ready to fire the Nano Forge. The Hydra was ready to deploy Omega Legion, the Hydra was destroyed within minutes, humiliating Earth and liberating Mars.