To this day the U.S. Naval Airship USS ZMC-2 remains unique in the history of lighter-than-air craft. Most airships fall under one of three basic construction formats: rigid, non-rigid or semi-rigid. However, the ZMC-2 employed a completely different construction method with a rigid, metal-covered envelope.
The most common airship type is the non-rigid, epitomized by today’s Goodyear blimps. These airships have a control car supported beneath a fabric-covered gas envelope, the shape of which is maintained by air-filled “ballonets.” The much larger rigid airships had a metal or wooden framework covered with fabric that enclosed a number of separate, individual internal were rigid airships. A semi-rigid airship had a gas envelope supported by a rigid wooden or metallic keel. The best-known examples were the and , constructed in Italy during the 1920s and employed for Arctic exploration.
