The main role of these craft was to escort convoys and scout or search for German U-boats.
[2] 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.
Designated the SST class, the first of 13 examples entered service in June 1918, and the last in May 1919, three of which, S.S.T.9, 11 and 12 were purchased by the US Navy.
[4] The SST used a larger 100,000 cu ft (2,800 m3) envelope than any of the other SS class types, and was equipped with a streamlined and waterproofed car that could accommodate a crew of five.
[4][5] At 57 mph (92 km/h), the SSTs had a greater top speed than all other SS class types, had the highest useful lift, and could stay airborne for up to two days.