Zeppelin III in flight, 1910.

GERMANY - APRIL 29: Ferdinand Graf von Zeppelin (1838-1917), began working on plans for a gas-filled airship after retiring from the military in 1873, and constructed his first dirigible in 1900. It had a rigid cylindrical frame covered in rubberised cotton and contained hydrogen-filled gas cells. It was steered by rudders and driven by two Daimler internal combustion engines. Although it was a technical failure, Zeppelin continued his research and in 1910 launched the first commercial air service for passengers. Zeppelins continued to be used in commercial flights until the late 1930s, when safety concerns after a number of disasters, including that of the �Hindenburg� in 1937, put an end to the airship�s popularity. (Photo by SSPL/Getty Images)