By 1838, steam-powered ships had crossed the Atlantic Ocean. This achievement was followed by three vital engineering advances that led eventually to the truly modern ship: the advent of metal construction, the switch from paddles to propeller propulsion, and reliance on the steam turbine for power. Initial experiments in the use of metal for ships started in the 1700s. John Wilkinson, the English iron-master, was a leading figure in the expanding iron industry and an important supplier of armaments in the middle and late eighteenth century. In 1787, he launched the first iron-hulled ship on the Severn River in England. Other English shipbuilders began to use iron, partially because good wood for ships was becoming scarce in their country. But iron had other advantages: it was stronger, safer, more economical, easier to repair, and lighter because wooden ships required huge timbers. With this final advantage, iron ships could...