During the War of 1812-1815, the United States put up a valiant fight against England’s Royal Navy, which at the time was the most powerful fleet in the world. The pride of the small American fleet were its powerful 50-gun frigates, which outmatched their British counterparts. By the end of the war, however, the Royal Navy had improvised a new type of warship, the razee (a third rate ship of the line with its upper gun deck “razed” or cut down to become a large fourth or fifth rate: frigates were considered fifth or sixth rate ships), to counter “pocket battleships” like the Constitution. By the end of the war, nearly all of the American squadrons were bottled up in harbor.
The Americans soon began to develop “secret weapons” to even the playing field: even though many of these infernal devices never saw action, they foreshadowed a different kind of sea warfare. Robert Fulton was coordinating many of these projects: he developed a sea mine as well as a submarine. However, his most dramatic project was the steam frigate Demologos, constructed in New York Harbor between 1813 and 1815 by the Brown brothers shipbuilders (Adam and Noah Brown, who had built Master Commandant O.H. Perry’s squadron on Lake Erie in 1813).
The Demologos was a giant catamaran, with a boiler and steam engine housed in two hulls. A paddlewheel set between the hulls propelled the vessel. It was built with five-foot oak walls and mounted 16 thirty-two pounder guns. She was also fitted out with lanteen-rigged sails to aid her primitive propulsion system. She was launched in October 1814. After the death of Robert Fulton in February 1815, the steam battery’s name was changed to Fulton, but she was completed too late to see action during the war.
Following the war, she served mainly as a receiving ship (a floating barracks) in New York, until she was blown up in a magazine explosion on June 4, 1829. The construction of her replacement, Fulton II, was supervised by Commodore Matthew Perry, the same officer who opened Japan to foreign trade.
Over the years there has been much speculation over what Demologos would have done had she encountered a British squadron. Although she was described as a steam frigate, in terms of mobility she would only have had an advantage over a becalmed sailing vessel. What she really was was a mobile fort, capable of moving herself to guard strategic points in a harbor. Forts were reckoned to have had an automatic advantage when engaging ships (having a stationary platform makes gunlaying easier, and you can’t sink or dismast a fort). It is doubtful that Demologos would have become the blockade breaker that Confederate ironclads were during the American Civil War (and even those screw-propelled ships were barely seaworthy).
In the end, Demologos’ significance was as a harbinger of the end of the age of sail. In the 1840s and 50s new steam warships, armed with shell guns and propelled by screws, would revolutionize naval combat. The introduction of armor plate and ever larger guns would dominate naval architecture, culminating in the Dreadnaughts and super-Dreadnaughts launched in the 1910s. By World War One, Fulton’s other infernal devices, the sea mine and the submarine, began to make capital ship fleets irrelevant: Britain's Grand Fleet spend most of the Great War cowering in Scapa Flow for fear of mines and torpedoes.