Editing Ship of the line (section)

===Steam power===
The first major change to the ship-of-the-line concept was the introduction of steam power as an auxiliary propulsion system. The first military uses of steamships came in the 1810s, and in the 1820s a number of navies experimented with [[paddle steamer]] warships. Their use spread in the 1830s, with paddle-steamer warships participating in conflicts like the [[First Opium War]] alongside ships of the line and frigates.<ref name=Sondhaus>Sondhaus, L. ''Naval Warfare, 1815–1914''</ref>

Paddle steamers, however, had major disadvantages. The paddle wheel above the waterline was exposed to enemy fire, while itself preventing the ship from firing broadsides effectively. During the 1840s, the [[Propeller|screw propeller]] emerged as the most likely method of steam propulsion, with both Britain and the US launching screw-propelled warships in 1843. Through the 1840s, the British and French navies launched ever larger and more powerful screw ships, alongside sail-powered ships of the line. In 1845, [[Henry Temple, 3rd Viscount Palmerston|Viscount Palmerston]] gave an indication of the role of the new steamships in tense Anglo-French relations, describing the [[English Channel]] as a "steam bridge", rather than a barrier to French invasion. It was partly because of the fear of war with France that the Royal Navy converted several old 74-gun ships of the line into 60-gun steam-powered blockships<!-- Note, the article "blockship" is about a different topic, please do not link to there. --> (following the model of [[Robert Fulton|Fulton]]'s {{ship|United States floating battery|Demologos||2}}), starting in 1845.<ref name="Sondhaus" /> The blockships were "originally conceived as steam batteries solely for harbour defence, but in September 1845 they were given a reduced [sailing] rig rather than none at all, to make them sea-going ships.… The blockships were to be a cost-effective experiment of great value."<ref>p. 30, [[Andrew Lambert|Lambert, Andrew]]. ''Battleships in Transition, the Creation of the Steam Battlefleet 1815–1860'', Conway Maritime Press, 1984. {{ISBN|0-85177-315-X}}.</ref> They subsequently gave good service in the [[Crimean War]].

[[File:Napoleon(1850).jpg|thumb|{{ship|French ship|Napoléon|1850|2}} (1850), the first steam battleship]]

The [[French Navy]], however, developed the first purpose-built steam battleship with the 90-gun {{ship|French ship|Napoléon|1850|2}} in 1850.<ref>"Napoleon (90 guns), the first purpose-designed screw line of battleships", ''Steam, Steel and Shellfire'', Conway's History of the Ship, p. 39.</ref> She is also considered the first true steam battleship, and the first screw battleship ever.<ref>"Hastened to completion Le Napoleon was launched on 16 May 1850, to become the world's first true steam battleship", ''Steam, Steel and Shellfire'', Conway's History of the Ship, p. 39.</ref> ''Napoléon'' was armed as a conventional ship of the line, but her steam engines could give her a speed of {{convert|12|kn|lk=in}}, regardless of the wind conditions{{snd}}a potentially decisive advantage in a naval engagement.

Eight sister ships to ''Napoléon'' were built in France over a period of ten years, but the United Kingdom soon took the lead in production, in number of both purpose-built and converted units. Altogether, France built 10 new wooden steam battleships and converted 28 from older battleship units, while the United Kingdom built 18 and converted 41.<ref>''Steam, Steel and Shellfire'', Conway's History of the Ship, p. 41.</ref>

In the end, France and Britain were the only two countries to develop fleets of wooden steam screw battleships, although several other navies made some use of a mixture of screw battleships and paddle-steamer frigates. These included Russia, [[Turkey]], [[Sweden]], [[Kingdom of the Two Sicilies|Naples]], [[Prussia]], [[Denmark]], and [[Austria]].<ref name="Sondhaus" />