[en] Nuclear powered ships possess the features of large power output, high speed, continuous navigation for long period, under water navigation and so on being realizable, accordingly, it is considered that they contribute largely to the future development of sea transport. The research and development of the nuclear powerd ship 'Mutsu' was started in 1963. Mutsu was completed in 1991, and thereafter, through four experimental voyages for one year, the valuable technical data were able to be obtained. Based on them, the research on the design of improved marine nuclear reactor and the preparation of the simulation system for nuclear powered ship engineering are advanced. The decommissioning works for the Mutsu is carried out at Sekinehama Port, and the reactor room containing the reactor is expected to be with drawn in a lump. All the circumstances of the research and development of the neuclear powered ship 'Mutsu' are described. As the future nuclear powered ships, those for ocean scientific investigation, the development of arctic route, the resource transport in Arctic Circle and high speed transport for long distance are conceivable, and the researches on large marine reactor MRX, the reactor for deep sea ships DRX, the simulation system for nuclear powered ship engineering and the systems for putting nuclear powered ships to practical use are carried out. (K.I.)