The design was intended to have a maximum speed of 17 knots using forced draft, but model testing of the hull showed that it could only reach . Rather than delay construction by redesigning the hull, the navy accepted the slower speed. Development of the quick-firing (QF) gun meant that an upper belt of armor was necessary and the weight required was gained by shortening the waterline armor belt, which left the ships' ends protected only by the sloping armor deck. Other changes included the replacement of the barbettes with turrets of the same type as used in the battleship and the substitution of QF guns for the original guns. This last change saved enough weight to permit four more six-inch guns to be added.