A drag reduction assembly is mountable on a vehicle or other object experiencing relative motion in a fluid environment. The assembly comprises at least one shell of flexible web material movable between non-deployed and deployed positions. In addition, the shell is configured to provide at least an outer flow surface in the deployed position (e.g., a curved surface) to reduce the effects of aerodynamic drag. In many embodiments, intake apertures such as NACA ducts may be provided to allow a portion of the flowing fluid into the shell. The flowing fluid will cause the shell to assume automatically the deployed position. In cases where fluid enters the shell, an exit location is provided in the shell to permit such fluid to exit and rejoin fluid on the outside.