High Quality Content by WIKIPEDIA articles! HMS Impregnable was a 98-gun second rate three-decker ship of the line of the Royal Navy, launched on 1 August 1810 at Chatham. She was designed by Sir William Rule, and was the only ship built to her draught. Purportedly as originally built she was a near copy of the famed first rate HMS Victory, Lord Nelson`s flagship at the Battle of Trafalgar.