Battle of Helm's Deep

The Battle of Helm's Deep was largely an event gone wrong, as the original plan was to have dragons attack random waypoints. Yet Sauron capitalized on the opportunity, and instead the event turned into two large battles in which dragons (loyal to neither side) were present.

Prelude
Though Sauron's forces had won many of the recent battles in the war, they had waited to take the fight to the Free Peoples until the opportune moment. That moment came when whispers spread of a dragon barreling towards Helm's Deep, and Sauron quickly dispatched his armies alongside the east Anduin whom marched unimpeded through Rohan and to the ancient fortress.

Battle
Though the battle began as a siege of Helm's Deep, the dragon's arrival pitted both the Free Peoples and Sauron's forces against the behemoth. After burning down much of the Deeping Wall, the dragon was abruptly slain by a wind lance fired by Reinwald. Legolas' troops quickly charged over the wall, making butcher's work of Sauron's troops.

Aftermath
Sauron's failed assault paved way for the retaliation against Mordor in the Fourth Siege of the Black Gate, and allowed the Free Peoples to once again test the speed at which they could rally their forces and prepare for battle. Yet Legolas was captured by a second dragon, whom flew him off to the pits of Udûn.