High Quality Content by WIKIPEDIA articles! HMS James Watt was a 91-gun steam and sail-powered second rate ship of the line. She had originally been ordered as one of a two ship class, with her sister HMS Cressy, under the name HMS Audacious. She was renamed on 18 November 1847 in honour of James Watt, the inventor of the steam engine. She was the only Royal Navy ship to bear this name. Both ships were reordered as screw propelled ships, James Watt in 1849, and Cressy in 1852. James Watt became one of the four-ship Agamemnon-class of ships of the line. They were initially planned as 80-gun ships, but the first two ships built to the design, HMS Agamemnon and James Watt, were rerated on 26 March 1851 to 91 guns ships, later followed by the remainder of the class.