Claudia units are what give all ships in Last Exile their power (they're engines). They're controlled by the Guild, and given out by the Guild. Whenever a ship is about to sink, or a side breaks the rules, or just because Delphine wants to, the Guild pulls a ships claudia unit.

They're operated from a small room below the main portion of the unit by Guild officials. Toward the end of the series, the Anatoray and Disith come up with a plan to break into their ship's units and capture them so that the units can never be taken away by the Guild. The operation is over all pretty successful with only a few ships losing their units.

There are only two ships that don't have guild controlled units: The Silvana and the Urbanus