A braking device for increasing the drag coefficient of an associated shell at a desired point while in flight is described. The device comprises: at least two braking vane means which, when released, extend substantially symmetrically into a surrounding airstream while said shell is in flight; retaining means for maintaining said at least two vane means in a retracted first position out of said airstream during an initial portion of said flight; releasing means to allow said at least two vanes to extend to a second position into said airstream at a desired point during said flight; said at least two vane means being extended by centrifugal force due to rotation of said associated shell about its axis; and, said at least two vane means further including co-operating means to ensure substantially symmetrical extension into said airstream.