comparison. Power operation was considered successful, although it was later implicated in the 1879 explosion. The Devastation-class ships had a complete wrought iron waterline armour belt that was 12 inches thick amidships and tapered to outside the armoured citadel towards the ends of the ship. The armour plates were tapered to a thickness of at their bottom edges respectively and they extended from the upper deck to below the waterline. The armoured citadel protected the bases of the gun turrets, the funnel uptakes and the crew's quarters. The sides of the citadel were 12 inches thick around the bases of the turrets and 10 inches thick elsewhere. The turrets were protected by two plates, separated by a layer of teak with the turret face having the thicker armour. The magazine were protected by a 6-inch forward bulkhead and a one aft. The conning tower ranged in thickness from 9 to 6 inches in thickness. The ships had a complete upper deck that was reinforced by another thick inside the citadel. Construction and careerThunderer, the fifth ship of her name to serve in the Royal Navy, was laid down on 26 June 1869 at Pembroke Dockyard, Wales. Construction was subsequently halted for a time in 1871 to modify the ship to improve her stability and buoyancy by extending the breastwork to cover the full width of the hull which increased the ship's freeboard amidships and provided additional accommodation for the crew. The ship was launched on 25 March 1872 by Mrs. Mary Meyrick, wife of Thomas Meyrick, MP. Two years later she was transferred to Portsmouth Dockyard to finish fitting out. On 14 July 1876, Thunderer suffered a disastrous boiler explosion which killed 45 people. One of her boilers burst as she proceeded from Portsmouth Harbour to Stokes Bay to carry out a full-power trial. The explosion killed 15 people instantly, including her commanding officer; around 70 others were injured, of whom 30 later died. This was the Royal Navy's most deadly boiler explosion through the whole century. A model representing the failed boiler was made and is now in the Science Museum, London. The explosion was caused because a pressure gauge was broken and the safety valve had corroded in place. When the steam stop valve to the engines was closed, pressure in the boiler rose and could not be released. The four box boilers were the last in service