To maximize the thickness of armor available for a given weight, it was desirable that the citadel be as small as possible. One way to achieve this was to concentrate the main battery in three turrets of triple or even two turrets of quadruple (quad) gun mountings, as opposed to four twin turrets typical during The First World War. In some cases, the turrets had an all-forward layout, such as the Royal Navy's and the French navy's . Another way is more compact and efficient machinery such as the French navy's use of "supercharged" "Indret" boilers for the "Dunkerque" class or the US Navy's decision to combine double-reduction gear turbines with extreme steam conditions (ultra high heat and pressure) in the , and .