The first item in this paper is a comparative review of the history of air and underwater achievements. We shall see that commercial underwater vehicles are a recent development and offer today a magnificent challenge to engineers with many opportunities and pitfalls. Small multi-disciplinary teams of engineers are able to advance rapidly, and the calibre of a few men matters, rather than vast organisations. In some ways this resembles the aeronautical world of the 1920s and 30s, during which period R. J. Mitchell contributed so greatly. Certainly it is closer to that period of aeronautics than to aerospace today, as I shall try to show.