Queen Death wanted to wipe out the Atlantis expedition which was a threat to her joined by Wraith factions. She launched a fleet of Atlantis after she learned the location of Dr. Rodney McKay which was converted to a Wraith known as "Quicksilver". (SGA: "The Lost")
Hive ships arrived to Atlantis and started their attack on the city. The Atlantis expedition responded to defend their city but discovered that the Hive ship uses an energy shield, something they have never before encountered a Wraith ship. The battle was long, but finally we managed Atlantis expedition to defeat the Wraith fleet.