A lighter-than-air semi-rigid airship has Configurable Buoyancy And Geometry (CBAG) allowing it to become short and plump for high buoyancy during takeoff and landing, but also allowing it to become long and slim for reduced drag (albeit less buoyancy) so that it may travel at high speed. It may be combined with a heavier-than-air structure having wings or rotors to form a hybrid aircraft whereby the wings or rotors provide enough lift to compensate for the reduced buoyancy during high-speed flight.