According to one embodiment, an apparatus includes a fluid coolant and structure which reduces a pressure of the fluid coolant through a subambient pressure at which the coolant has a cooling temperature less than a temperature of the heat-generating structure. The apparatus also includes structure that directs a flow of the fluid coolant in the form of a liquid at a subambient pressure in a manner causing the liquid coolant to be brought into thermal communication with the heat-generating structure. The heat from the heat-generating structure causes the liquid coolant to boil and vaporize so that the coolant absorbs heat from the heat-generating structure as the coolant changes state. The structure is configured to circulate the fluid coolant through a flow loop while maintaining the pressure of the fluid coolant within a range having an upper bound less than ambient pressure. The apparatus also includes a first heat exchanger for exchanging heat between the fluid coolant flowing through the loop and a second coolant in an intermediary loop so as to condense the fluid coolant flowing through the loop to a liquid. The apparatus also includes a second heat exchanger for exchanging heat between the second coolant in the intermediary cooling loop and a body of water on which the ship is disposed.