The ability of elastomers to store large quantities of energy, which can subsequently be recovered very quickly, makes them attractive materials for propulsion devices. Recently the U.S. Navy has developed a torpedo ejection system based on an elastomeric mechanical capacitor. The criteria governing selection of a material for this application include high elastic energy, sufficient fatigue life, minimal creep, and resistance to deterioration by seawater. This paper describes various approaches to obtaining these material properties.