The map above shows the Drilltruck and a Hovertruck on the underground layer after travelling down the elevator from the surface layer.  The best way of winning this mission is by constructing the Defense Relay string underground to avoid a formidable enemy force on the surface.  The Drilltruck should be sent to drill a tunnel system that leads beneath the Archeology Station, so that Hovertrucks can build and link Defense Relays along the path.  To command the Drilltruck to drill, simply select the Drilltruck and point the cursor to an area on the playfield that turns the cursor into a spinning drill icon or just right-click an area on the minimap.