This paper presents a systems study of thermal energy storage and suggests its application for submarine propulsion. The basis for considering unconventional propulsion methods as well as a review of certain desirable characteristics is given. Familiar examples and commercial applications are offered as historical evidence of the feasibility of these concepts. Thermal energy storage using heat of fusion of various elements and compounds and sensible heat of certain refractories is compared, based on weight and volume moduli, with potential and kinetic energy systems. A study is also made of the advantages and disadvantages of thermal energy derived from chemical reactions as well as physical changes of state. Heat exchangers as well as thermodynamic and transport properties of heat transfer media are discussed. Rankine, Brayton and Stirling cycles are examined for their applicability with heat storage and submarines. Analyses of charging and conversion systems and efficiencies are made. A hypothetical submarine and a proposed propulsion system is presented, including assumptions and calculations of speed and range for heat storage compared to a battery-electric system.