Steam-powered screw frigates were built in the mid-1840s, and at the end of the decade the French Navy introduced steam power to its line of battle. The desire for change came from the ambition of Napoleon III to gain greater influence in Europe, which required a challenge to the British at sea. The first purpose-built steam battleship was the 90-gun in 1850. "Napoléon" was armed as a conventional ship-of-the-line, but her steam engines could give her a speed of 12 knots (22 km/h), regardless of the wind conditions: a potentially decisive advantage in a naval engagement.