Iron SyISS

The ISS as it appeared in the film

The International Space Station was a weaponised spacecraft used by the European Union during the battle against the invading Nazi forces. It is, obviously, based on the real-life ISS.

The ISS was seen arriving to reinforce the USS George W. Bush. It was later destroyed when it collided with the Götterdämmerung.

The ISS had a "revolver" as a main weapon [1], although the exact effects and type of this weapon are unknown, and the ISS is actually never even shown firing it's weapon on-screen.

Based from the structural appearance of the ISS it might be a support ship