The Zeppelin NT is a class of helium-filled airships being manufactured since the 1990s by the German company Zeppelin Luftschifftechnik GmbH (ZLT) in Friedrichshafen. The initial model is the NT07. The company considers itself the successor of the companies founded by Ferdinand von Zeppelin which constructed and operated the very successful Zeppelin airships in the first third of the 20th century. There are, however, a number of notable differences between the Zeppelin NT and the airships of those days, as well as between the Zeppelin NT and usual non-rigid airships known as blimps. The Zeppelin NT is classified as a semi-rigid airship.