1. A lightweight, compact portable body heating system, said system comprising: a body protective suit having a liquid therein; and a heater including; an inner casing containing a material having a high heat of fusion, heating means operatively associated with said inner casing for charging said material with heat, a closed, recirculating conduit means surrounding said inner casing permitting recirculating liquid flow about said casing whereby said liquid is heated by said heat of fusion of said material, said conduit means comprising an inlet tube and an outlet tube, an inlet plenum coupled to said inlet tube, an outlet plenum coupled to said outlet tube, said inlet plenum being interconnected with said outlet plenum through a plurality of tubes, said plurality of tubes encircling said inner casing and being coaxial therewith, whereby heated liquid is passed to said body protective suit through said outlet tube and recirculated through said inlet tube to said inner casing; pump means for regulating fluid flow through said conduit means, means for actuating said pump means; and a thermoelectric power source including a plurality of thermocouples having their cold junctions positioned in heat exchange relationship with said outlet plenum and their hot junctions positioned in heat exchange relationship with said inner casing; said pump means being electrically actuated and being electrically coupled with said thermoelectric power source for operating said pump means.

4. A lightweight, compact, porTable body heating system, said system comprising: a body protective suit having a liquid therein; and a heater including; an inner casing containing a material having a high heat of fusion, heating means operatively associated with said inner casing for charging said material with heat, said heating means including a radioisotope charge located in said material having a high heat of fusion, a closed, recirculating conduit means surrounding said inner casing permitting recirculating liquid flow about said casing whereby said liquid is heated by said heat of fusion of said material, said conduit means comprising an inlet tube and an outlet tube, an inlet plenum coupled to said inlet tube, an outlet plenum coupled to said outlet tube, said inlet plenum being interconnected with said outlet plenum through a plurality of tubes, said plurality of tubes encircling said inner casing and being coaxial therewith, whereby heated liquid is passed to said body protective suit through said outlet tube and recirculated through said inlet tube to said inner casing, pump means for regulating fluid flow through said conduit means, means for actuating said pump means, and a thermoelectric power source including a plurality of thermocouples having their cold junctions positioned in heat exchange relationship with said outlet plenum and their hot junctions positioned in heat exchange relationship with said inner casing, said pump means is electrically actuated and is electrically coupled with said thermoelectric power source for operating said pump means.