Omega Base is a research facility for SHIELD.
The Omega Base is a mobile S.H.I.E.L.D research facility that is multiple stories tall. S.H.I.E.L.D. used to field test highly classified experiments, some of which include the Gamma Bomb, the Super Soldier Serum, and the Neural Inhibitor. Also, Dr. Hank Pym was working on the Cybernetic Helmet. There was also a computer containing data on the Legacy Virus.
Marvel: Ultimate Alliance: Story
The base was attacked by the Masters of Evil and was sent on a crash course with Vondrak Dam. While trying to stop it, the New Avengers confronted M.O.D.O.K. who was apparently controlling the direction of the base. After defeating M.O.D.O.K., the Avengers stopped the Omega Base from crashing into the Vondrak Dam and returned to Stark Tower for their next mission.