After an earlier, failed attempt to take Altair the Romulans once again try to take it after their defeat at Berengaria. However, Altair VI was defended by one of the largest fleets assembled by the Coalition during the war, and majority of these vessels were Andorian and Tellarite.
In a battle which lasted just under 10 minutes, Romulan forces engaged those of the Coalition in a brutal battle destroying large portions of the Coalition fleet. During the battle, the portside hull plating of the Endeavour was melted off by a salvo of nukes. The Romulan vessels managed to gain remote control of several Coalition ships, but those were quickly destroyed by their own crews. On top of this, the Romulan forces were so out numbered, that they simply couldn't hijack enough ships in time to make a difference for them.
This battle come on the heels of the Second Battle of Berengaria helping raise the spirits of Earth. Unfortunately, the heavy losses sustained by Tellarite and Andorian forces caused both governments to reconsider their participation in the war effort, leading to their witdrawal. (ENT - The Romulan War novel: Beneath the Raptor's Wing)