An airship is a type of aircraft that is filled with helium or hydrogen gas and has a rigid structure, typically in the form of a long cylinder. Airships are designed to float in the air and can be steered by adjusting their direction of travel through the use of engines and rudders. They were once used for various purposes such as transportation, surveillance, and bombing missions during World War I. However, after several accidents and advancements in other forms of aviation, airships are no longer widely used for commercial or military purposes.