On the Astral Plane, the githyanki commonly wage war from massive astral ships. Such vessels can be equivalent in size to anything from a small keelboat with room for a single squad of soldiers to a massive galleon that can carry hundreds of troops. Powered by magic sails that catch the motion of astral energies, these ships are normally useless on the Material Plane, where no such archane winds blow.
For centuries, however, the githyanki have worked together to create magic items that allow certain astral ships to fly through the skies of a Material Plane world. Armed with a spine of earthly wind, an astral vessel can sail through a portal into the Material Plane and darken the sky of your game world. For information about astral ships and other githyanki modes of travel, see Dungeon #100. More vehicle rules can be found in Dragon #294 and the Arms and Equipment Guide.