The Astra-Torres airships were non-rigid airships built by Société Astra to a design by Spaniard Leonardo Torres Quevedo in France between about 1908 and 1922. They had a highly-characteristic tri-lobed cross-section rather than the more usual circular cross-section. This was the result of moving most of the blimp's bracing wires inside the envelope in an attempt to minimise drag. Early Astra-Torres airships could be trimmed by moving the entire gondola fore-and-aft.
Astra-Torres airships were used by the French Navy during World War I and for a few years before and after. A few of these were transferred to the American expeditionary forces in Europe, and AT-1, AT-13, and AT-17 were eventually taken back to the United States.
Britain's Royal Navy purchased AT-14, AT-17, and AT-19, these becoming HMA No. 3, HMA No. 8, and HMA No. 16 respectively. All were taken out of service in May 1916, although the Astra-Torres design was imitated in Britain's own Coastal class blimps that served through to the end of the War.
After the war, AT-16 was operated by Transaérienne, carrying sightseeing passengers over Paris, and AT-24 was purchased by the Japanese Navy.
British Admiralty and Imperial Airship Scheme airship designations
Before 1915, each rigid and non-rigid airship was given a place in this numerical sequence. Later, these individual numbers were only assigned to rigids, with non-rigids organised into their own classes.