In 1919 France was allocated the uncompleted battlecruiser SMS Graf Spee, at that stage 75-80% complete. The hull was completed, machinery fitted (never run), but no main armament had been received and only a few guns of the secondary and tertiary weapons had been mounted. The main weapons had been purloined for mounting as rail guns for the Western Front. The ship was towed to Brest where it sat gathering rust till 1923 when plans were finalised for what to do with the ship. Many ideas had been bandied about as to armaments and uses. Mount the available 13.4" guns (from the uncompleted Normandie class), which would require a new twin mounting to fit the German barbette. Scrap it. Produce a new 14"-to-15" type gun that could be fitted into the existing barbettes. Turn it into an Aircraft Carrier. By 1923 all of the Major Powers were converting or building the new type of ship. France had the Bearn under conversion, which would be fast enough to act with the current battlefleet. A faster unit, to match the UK and US conversions, that could act with the scout units was deemed necessary.
The conversion proceeded slowly and was finally completed late in 1928. The ship resembled the Bearn strongly (not a surprise). On commissioning into the French Navy the ship was renamed 'Guynemer' to commemorate Frances leading fighter pilot of WW1. The ship was used to trial many features during its initial service. In 1938 the ship was taken in hand for modernisation. This was not contemplated for Bearn which was deemed too slow to warrant the expense. It was good enough to act with the old Lorraine class ships as is. The Guynemer however was right for updating as it could then act with the new Dunkerque class battleships.
The drawing below shows the ship in its final version with single 5.1" and 25mm AA guns. (I have shamelessly pinched the aircraft from GD's Neptune)