This fifth edition has been thoroughly revised and many of the chapters have been rewritten to take account of the drastic and revolutionary changes in marine electrical practice over the past two decades. One of the most important changes has been the almost complete elimination of dc in favour of ac although the former is still used in very small ships. In view of this the chapter on dc generators has been considerably shortened and the space used to include revised and expanded material on ac generators, switch gear, and distribution systems. The revised chapter on dc generators will however, still be of interest in relation to older installations, small ships and for main propulsion (electric) systems. The subject of electro-magnetic compatibility (ie interference) has been receiving ever-increasing attention and this is applicable to marine electrical installations as well as to those which are shore-based. A separate chapter has now been added on this subject which covers possible cases of interference and how to avoid these by careful planning of the installation. Many developments have taken place in the manufacture of cables for marine purposes. Rubber, and lead-sheathed cables have now been almost eliminated in favour of new types of covering using clastomeric compounds. In consequence of this the chapter on cable installation has been completely re-written to include up-to-date information on cabling. Recent years have seen the advent of the so-called unmanned engine room and also the introduction of super-tankers. In view of these changes, the tanker section has been completely re-written by Mike Carlisle of Shell Tankers who is a well-known expert on this subject. This chapter now reflects the current thinking on electrical equipment installed in tankers from the important safety aspect.