Lincoln Memorial. Army blimp over Lincoln Memorial with construction materials for Memorial Bridge in foreground

The main types of airship are non-rigid, semi-rigid, and rigid. Non-rigid airships, often called "blimps", rely on internal pressure to maintain the shape of the airship. Semi-rigid airships maintain the envelope shape by internal pressure but have a supporting structure. Rigid airships have an outer structural framework which maintains the shape and carries all structural loads, while the lifting gas is contained in internal gas bags or cells. Rigid airships were first flown by Count Zeppelin and the vast majority of rigid airships built were manufactured by the firm he founded. As a result, all rigid airships are sometimes called zeppelins. In early dirigibles, the lifting gas used was hydrogen, due to its high lifting capacity and ready availability. Helium gas has almost the same lifting capacity and is not flammable, unlike hydrogen, but is rare and relatively expensive. Airships were most commonly used before the 1940s, but their use decreased over time as their capabilities were surpassed by those of aeroplanes.

Airplanes and blimps above National Mall, Washington Monument, Potomac river and around.

Blimp a large aircraft without wings, consisting of a large bag filled with gas that is lighter than air and driven by engines. In the past passengers were carried in a structure hanging below. In 1852, Henri Giffard built the first powered airship, which consisted of a 143-ft (44-m) long, cigar-shaped, gas-filled bag with a propeller, powered by a 3-horsepower (2.2-kW) steam engine. Later, in 1900, Count Ferdinand von Zeppelin of Germany invented the first rigid airship.