Earth vessel believed to be crewed by the Chinese, similar to how Russia was granted full command of the Korolev thanks to both country's participation in the Gate Alliance Treaty. Named for the legendary strategist, the Sun Tzu is presumably a BC-304-class deep space carrier. It followed the Korolev in production order and preceded the George Hammond. Like other ships in its class it is likely equipped with advanced Asgard weapons, shields, and transporters.
When the Atlantis expedition learned that an enhanced Wraith hive ship was en route to attack Earth the Sun Tzu joined the Apollo in intercepting and engaging the enemy craft in the void between the Milky Way and Pegasus Galaxies. They were severely outmatched and the Sun Tzu was disabled -- so badly that it was venting its atmosphere, forcing the ship's crew to evacuate to its sister ship.
It is not known if the Sun Tzu was abandoned in the void or later repaired and recovered.
Note: As the Sun Tzu did not appear on screen, a BC-304 vessel believed to be identical is pictured above.
Enemy At the Gate - Alongside the Apollo, the Sun Tzu is crippled when the ships confront a Wraith super-hive in the void between galaxies.