An Aldis Lamp is a light that is used to signal between ships using a code based on "lamp on" and "lamp off" of various lengths of time and frequencies. While there may be a common signal code among similar states, as with the Periphery and Torumekia, for example, each military presumably has its own secret codes.
The Dorok Air Monitor signals to the Valley Gunship with an Aldis Lamp [1].
Worm Handlers on the Worm Handler Brig use an Aldis Lamp [2] to signal a pair of Dorok Air Monitors.
Torumekian airships use an Aldis Lamp [3] to signal to other Torumekian airships.
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a See Page Conversions Between Editions to convert Deluxe Edition volume 1 (DE1) to other editions