armour at the muzzle. The ships were equipped with four RML 6 in (152 mm) 71 cwt guns as chase guns, two in the bow and another pair in the stern. They fired a , shell. They also had six RBL 20 pdr rifled breech-loading guns that were used as saluting guns. In 1878, the ships received four torpedo launchers on the main deck and the 6-inch guns were replaced by four breech-loading BL 5-inch guns during the mid-1880s. The wrought iron waterline armour belt of the Audacious class covered the entire length of the ships. It was thick amidships, backed by of teak, and thinned to six inches towards the ends of the ships. It had a total height of of which was below water and above at deep load. The main deck citadel's ends were protected by a forward bulkhead and a one aft. The sides and embrasures of the upper battery were six inches thick, but its ends were unprotected. The ships also had a one-man conning tower with walls thick. Construction and career Iron Duke, named after the nickname for Arthur Wellesley, 1st Duke of Wellington, was the first ship of her name to serve in the Royal Navy. The ship was laid down at Pembroke Dockyard on 23 August 1868, launched on 1 March 1870 and was completed on 1 January 1871, at a cost of £208,763. She was initially assigned as a First Reserve Guardship at Plymouth, but was assigned as the flagship of the China Station in September. En route to the Far East, she became the first ironclad to use the Suez canal; virtually all of her coal had to be unloaded to reduce her draught and she was towed by three tugboats through the canal in three days. Relieved by her sister ship, , Iron Duke returned to the UK in 1875. To save money on the return ship, no tugboats were hired and the ship ran aground four times and frequently scraped the sides of the canal during her four-day transit. Upon her arrival, she was paid off in May. Iron Duke recommissioned two months later and was assigned as the guardship at Hull. During the First Reserve Squadron's summer cruise on 1 September, she was en route with three other ironclads between Dublin and Queenstown (now Cobh). In a thick fog, the ship accidentally rammed her sister, Vanguard, off