The ships' main battery turrets sides and faces were thick—reduced slightly compared to earlier ships to account for the heavier belt armour—with thick rears. The turret roofs were 3 in thick. The turrets sat atop 12 in thick barbettes, though "Irresistible"s barbette armour was reduced in thickness to 10 in behind the belt. Above the main belt was a strake of armour that protected the casemate guns, which was 6 inches thick; behind the casemates, an interior bulkhead that was thick protected the interior of the ship. Their forward conning tower had thick sides, with a communication tube below the tower that had armour protection that was thick. The aft conning tower had 3 in thick sides with a 3 in tube below.