Originally, the Panel considered only water-cooled and moderated reactors and prepared Technical and Research Bulletin No. 3-6 which was published by the Society in March 1959. In 1962, it was decided to study similar safety recommendations for organic-cooled and moderated reactors and gas-cooled reactors. As a result of these studies, it was determined that Bulletin No. 3-6 should be revised to make the recommendations applicable to the reactor types currently under consideration for marine applications and to bring them up to date. This Bulletin, therefore, supersedes Bulletin No. 3-6. It is of particular importance to understand that these recommendations are intended as a guide to supplement the requirements of the cognizant government regulatory agencies and classification societies. Based on its work, the Panel has concluded that nuclear reactors can provide safe, reliable propulsive power without imposing unrealistic operational restrictions upon the nuclear ships in which they are installed.