Abstract: An active heating system for an underwater diver uses material particles that can generate heat in an exothermic reaction in the presence of oxygen. The material particles are positioned at selected region(s) within an underwater diver's attire. A source of oxygen gas is coupled to the selected region(s).

Abstract: The invention is a submersible hand warmer apparatus for warming a diver's gloved hands. The apparatus includes a sleeve having a center portion with an elongate chamber with a right access port and a left access port; and right and left sleeve portions with elastic cuffs. The cuffs can be stretched allowing the diver's gloved hands access to the chamber, and then retract, forming a seal against the diver's arms. The chamber is sized for enough heat transfer fluid, such as water, so that the temperature of the diver's hands is raised to at least 54° F. upon immersion of his hands in the water. The apparatus also includes a heating component; an energy source, such as a battery; a housing which provides structural support; an insulation that slows the loss of heat to the cold ambient water; and a controller that controls the rate that energy is consumed.