The SST (Sea Scout Twin) class of non-rigid airship or "blimp" was developed in Great Britain during World War I from the earlier SS class airship. The main role of these craft was to escort convoys and scout or search for German U-Boats.Designs were submitted in 1917 for a twin-engined SS class airship, the idea being that should there be an engine failure, the craft would not be rendered helpless and therefore less likely to be lost.