Dirigibleor Airship, a balloon that is self-propelled and that can be steered. There are three types: (1) the rigid dirigible, which holds its shape by means of a rigid metal framework around the gas cells; (2) the semirigid dirigible, which has a rigid keel along the bottom inside a single fabric gas bag, known as the envelope, but no framework around the envelope; and (3) the nonrigid dirigible, which holds its shape only by the pressure of the gas inside the fabric envelope. This article is concerned with rigid and semirigid dirigibles. Nonrigid dirigibles are discussed in the article Blimp.
Dirigibles were used as military weapons in World War I and as passenger and cargo ships from 1910 to 1937. The dirigible's main advantages over airplanes of the same period were lifting power, long range, and the ability to hover. However, dirigibles did not approach the speed of airplanes. Except for blimps, no dirigibles were used during World War II. Airplanes have completely replaced dirigibles for carrying passengers and cargo.