Foch abandoned the small coal-fired boilers, gained additional fuel-oil capacity, and changed her mast and external arrangements. Dupleix then returned to aspects of the earlier mast layout while adopting twin 90 mm mounts. These were meaningful production changes within the same operational concept. French records still treated the four vessels as one class, so the class label could absorb machinery and fitting revisions between sisters. The Suffrens were an evolving production family rather than a set of perfectly identical hulls.
Chapter · 47:25-47:59
One class, four incrementally different cruisers
Foch and Dupleix altered machinery, fuel storage, masts, and secondary batteries without breaking the French view that all four ships formed one evolving class.