Lightships guided ships of all nations past offshore reefs and sandbanks that posed extreme hazards to navigation where lighthouses could not be built. This book describes their design, construction and evolution over more than two centuries of service. Originally constructed from teak, they progressed through iron hulls to steel. Their lights burnt whale oil, colza oil, then paraffin before electricity provided the greatest brightness. Fog warnings were given by bells, gongs, reed horns and sirens before reaching maximum power with the diaphone, which could be heard up to 10 miles away. All these features, most of which resulted from major scientific and engineering advances made in the nineteenth century, are examined here. For hundreds of years lightships made the sea lanes around Great Britain far safer for navigators. Their history and development are well documented through the rare images and detailed information contained within this book.