plate 21 and plunger 30 to their fully extended position the application of electrical energy can then be discontinued either by operation of circuit switch 36 being reset by the passage of the expansion end plate 21 or manual resetting of switch 18 when it is desired to retract plunger 30 electrical energy is applied to retractor memory shape element 11 by the setting of switch 18 the transformation of retractor memory shape element 11 to the austenitic state moves retractor end plate 25 and plunger 30 to its innermost position within the actuator 10 as the retractor end plate passes circuit switch 35 or switch 18 is reset the supply of electrical energy is interrupted and retractor memory shape element 11 returns to its martensitic form and the system is again at rest a further embodiment of the actuator of this invention is schematically shown in fig3 in this embodiment the actuator 40 comprises an outer housing 41 to which cover plate 42 is attached a plunger or movement arm 43 extends through the cover plate 42 one end 44 of the plunger 43 is attached a plate 45 the opposite end of the plunger 43 which extends through cover plate 42 is attached to retractor shape memory element 46 which will form a retractor spring when in the austenitic state an expansion shape memory element 47 which will form an expansion spring when in the austenitic state is secured to plunger 43 opposite memory element 46 the actuator is supplied.