Today's Navy ship propulsion fuel has evolved from coal used to generate steam in the pre-World War I fleet through several residual fuel oils to the present Naval Distillate Fuel suitable for powering boilers, diesels, and gas turbines. The Navy's mission imposes unique requirements upon its shipboard fuel. The fuel must be suitable for use in any of the various ship propulsion systems found in Navy ships (boiler-steam turbine, diesel, and gas turbine systems). Further, the fuel must be suitable whether the particular ship is operating in the Arctic or in tropical waters, or whether the ship is in quiet transit or is conducting battle maneuvers. The fuel also must remain suitable for use whether it has been in storage for a short or long time. These special operating requirements necessitate the specification of more chemical and physical property limitations than are required for normal commercial fuels. Naval Distillate Fuel delivered to the Navy during the 1979 to 1982 period showed a slight but definite trend toward poorer quality with respect to such properties as cetane number, storage stability, carbon residue, and gravity. A survey among suppliers of Navy fuel together with forecasts by industry members of the U.S. delegation to the Quadripartite Navies Information Exchange Program indicated that a general worsening of middle distillate fuel quality can be expected through the year 2000 A.D. Heavier crudes containing higher levels of sulfur and yielding larger volumes of residuum will necessitate greater use of cracking processes to produce the increasing demand for middle distillate fuels, which are expected to reach 40% of the refinery product slate by 2000 A.D. Engine designs will evolve to accommodate the poorer quality fuel and the subsequent increased engine maintenance requirements.