Dirigibles, also known as airships, are large, buoyant aircraft that are filled with gas, such as helium or hydrogen, to achieve lift. They have a rigid or semi-rigid structure and are typically propelled by engines. Dirigibles can travel slowly and are often used for advertising, surveillance, and tourism. The most famous dirigible is the Hindenburg, which was a German passenger airship that tragically caught fire in 1937. While dirigibles were popular in the early 20th century, their use declined due to safety concerns and the rise of faster airplanes. Today, they are mainly used for specialized purposes.