 The armour protection given to the Lions was heavier than that of the Indefatigables; their waterline belt of Krupp Cemented Armour measured 9 inches (229 mm) thick amidships in contrast to the 6-inch (152 mm) belt of their predecessors. It thinned to four inches towards the ships' ends, but did not reach either the bow or the stern. In addition they were given an upper armour belt with a maximum thickness of six inches over the same length as the thickest part of the waterline armour and thinned to 5 inches (127 mm) abreast the end turrets. Four-inch transverse bulkheads closed off the ends of the armoured citadel. Nickel-steel plating was used for the protective decks. The lower armoured deck was generally only 1 inch (25.4 mm) thick except outside the citadel where it was 2.5 inches (64 mm). The upper armoured deck was situated at the top of the upper armour belt and was also only one inch thick. The forecastle deck ranged from 1.25 to 1.5 inches (32 to 38 mm).
