Navies once had to depend on the kindness of winds to move them towards their destination--but, in one of the most dramatic changes in military machinery, the ironclad, steam-powered ship took over. This new armored warship ensured British invincibility at sea, and secured for them the most extensive empire ever known. But, the English were not the lone beneficiaries of these new battleships: they also proved crucial during other wars, as well, including the American Civil War. With the help of over 150 illustrations and color maps, including computer-generated cartography, an eminent former Rear-Admiral in the Royal Navy describes the changes in technology that led to these supreme instruments of sea warfare, the evolution in weapons and tactics, and the strategies that forever transformed conflict on the high seas.