the fin at the proper incidence may be made by means of a piston actuated by gases generated by a charge placed on board the missile and fired by an electrical firing mechanism or a mechanical striking pin the deformation part 5 can absorb energy in many ways the first way corresponds to the embodiment shown in figure 2 in this case this compression piece 4 has a tubular shape reinforced at its ends so that it represents a flattened u when this part is compressed its central part is buckled and the material of this central part partially filling the inside of the u the materials used may be copper or aluminium or any relatively malleable or ductile alloys with reference to fig3 a and 3b the compression ring 34 and the deformation part 35 have shapes different from those of the previous embodiment the compression ring 34 is still free in translation and fixed in rotation so as to be displaced towards the deformation part 35 the deformation or change in shape as such does not take place in the same way because the deformation part although it is still tubular has a more compact shape and its internal diameter is suited to axis 31 it is still supported on the radial surface 15 of the first bearing 33 however the opposite end receives the action of the compression ring 34 which moves towards the deformation part 35 the longitudinal compression caused by the buckling of this latter part is no longer possible owing to the compactness of this part since there is a space 36 defined between the external diameter of the compression ring and the.