"Warrior" was ordered on 11 May 1859 from Thames Ironworks and Shipbuilding Company in Blackwall, London. The ship was laid down some time after 6 June 1859 on the West Ham side of Bow Creek when the P&O ocean liner "Seine" was launched, and the slipway was reinforced to support "Warrior"s weight. Full-scale production of the ship's iron began in August, and the construction probably began in mid-August. Indecision by the Admiralty and frequent design changes caused many delays and nearly drove her builders bankrupt before a grant of £50,000 was awarded to keep them solvent. Her launching on 29 December 1860 was during the coldest winter for 50 years. She was frozen to her slipway and required the use of hydraulic rams, additional tugs, and dockworkers running from side to side on the upper deck to rock her free. "Warrior" was commissioned in August 1861 to conduct her sea trials; she was completed on 24 October for £377,292, almost twice the cost of a contemporary wooden ship of the line. Between March and June 1862, defects exposed during her trials were rectified, and damage repaired. Changes included the fitting of a lighter bowsprit and a shorter jib boom, along with the provision of extra heads amidships.