The first application of steam power to vehicles was at sea, where the Ironclad and the Monitor can be built to dominate the oceans and defend your own coasts.
The earliest primitive steam engine was built by Heron of Alexandria around 100 BC as a novelty. Thomas Newcomen built the first useful working steam engine in England, in 1705 - 1712 to pump water out of deep mines. Even after improvements in the early part of the 18th century, these were large, low-powered static machines. In 1765 James Watt developed a condenser that vastly improved the efficiency of the Newcomen-type engine, and after 1775 Wilkinson’s new boring machines made production of steam engines an economic practicality. Steam power replaced waterpower to run textile machinery in a mill for the first time in 1785, and steam-powered boats were being built in both England and the United States in 1788. Commercial river steamboat travel started in 1802, the first steam locomotive hauled cars around a track in 1804, and the first scheduled ocean steamship entered service in 1812. Steam power for warships solved an old, old problem for navies: even if a ship could be armor plated, how to protect the propulsion system that consisted of either banks of oars or towering masts laden with canvas? Since the steam engine and driving propeller could be encased within or under the hull, the modern armored warship or Ironclad dates from the application of the steam engine to naval warfare. The first armored steam-powered warship was, in fact, Robert Fulton’s "Demologos", launched in 1813, and by the Crimean War both England and France used armored ’floating batteries’ against the Russians at Sevastopol.
One of the most innovative warships of all time was the USS Monitor, designed by John Ericsson of Sweden and launched in 1862. Among the firsts in this warship, it had the first rotating turret for its main armament, screw propellers, forced draft exhaust, and ventilation system for a ship that was almost entirely below the waterline. Although not very suitable for the high seas (the Monitor herself sank in a gale off the American coast) monitors were built extensively for coast defense and the term Monitor in the twentieth century was applied to any shallow-draft big-gun vessel for riverine or coast defense work.