Battleangel

Via GameSpy: PlanetSide Expansion Media

This is what they have to say about it:
- Six new massive underground war zones
- New Ancient-technology vehicles and weapons which can be used by all Empires
- Head-to-Head Urban style combat in subterranean cities
- Unique alien complexes to explore and conquer
- New underground environments from volcanic lava flows to ice caverns
- Ancient technology can be used by all Empires to upgrade existing surface level facilities

So, basically 3 new weapons that all can use. And 3 new vehicles with the same purpose. It is somewhat curious why Sony chose to make an expansion so soon. Maybe interest in the original game has been dwindling. Core Combat is available for beta testing .. but ONLY to PlanetSide subscribers. Tough luck.