A lighter than air blimp which has either an aerodynamically shaped or a round envelope of flexible sheet material, and a plurality of stabilizing fins mounted in a circumferentially spaced apart arrangement about the tail end portion of the envelope. The tail fins are collapsible, to faciliate storage and transport to the point of use, and to also facilitate the rapid assembly and deployment of the blimp at the point of use, particularly under windy conditions. The tail fins are attached while the envelope is deflated and with the fins in a collapsed position, and after the envelope is inflated, the fins can be moved to snap upwardly to an operative position.