The second HMS Mersey was commissioned in 1858, just six years after the first Mersey had been broken up. She and her sister ship the Orlando were the longest wooden warships built for the Royal Navy. At 336 feet in length, HMS Mersey was nearly twice the size of HMS Victory, the flagship of Admiral Horatio Nelson at the Battle of Trafalgar. At 5643 tons displacement, she was certainly a large and impressive looking ship in her day. She was heavily armed, and in comparison to many of her counterparts was quite fast with an approximate speed of 12½ knots, achieving 13½ on trials.