The correct answer is B) Greater heat energy available per pound of steam. Superheated steam has a higher temperature than saturated steam at the same pressure, which means it contains more heat energy per pound of steam. This additional heat energy can be converted into more mechanical work in the main propulsion turbines, improving the overall efficiency of the propulsion system. The other answer choices are incorrect because: A) Superheated steam has a greater specific energy available per pound compared to saturated steam. C) The higher pressure available with superheated steam is a consequence of the greater heat energy, not a primary reason for its use. D) The lower specific volume of superheated steam is also a consequence of the greater heat energy, not a primary reason for its use.