Like so many towns and cities, Portsmouth has undergone numerous changes since the Second World War, having to accommodate the car, replace many old and outworn houses, accept the demise of old established industries, and come to terms with dramatic change in retailing, which has seen the demise of many small food shops and general stores and the rise of the supermarket and superstore. But Portsmouth is essentially a maritime city, a very special one at that, for at its centre - indeed the reason for its existence - is the naval dockyard. For centuries the town flourished in times of war, but the introduction of missiles and nuclear submarines in place of many conventional craft caused employment to fall from 25,000 in the early 1950s to 2,000 at the end of the twentieth century. Yet against all expectation this contraction has been absorbed without undue difficulty.