M-DTEC is precisely the same as OTEC theory and technology, utilization of waste heat energy. The fossil fuel consumption on ships will be kept at minimum in proportion to the effective use of waste heat energy. This is the Earth-friendly energy saving technology. Efficiency of diesel engine has been greatly improved. There are those engines with more than 50% in its single efficiency. Nevertheless, the other half of its energy is being wasted as in the form of exhaust gas or dissipated into the cooling medium of seawater. Waste heat recovery from steam generator and turbine is not a new challenge, but the fact that the greatly improved efficiency of diesel engine was attained by lowering the level of waste heat temperature had presented new technical difficulties to induce investment for energy recovery system. Now, M-DTEC by Uehara cycle has made it possible to recover not only waste heat energy of exhaust gas but also those from air-cooler and cylinder jacket of diesel engine and even that from lubricating oil, which had been difficult to deal fro recovery. Uehara cycle shall contribute in the shipbuilding industries by converting all types of ships, large and small, to environment-friendly ships with saving of energy.