[Laurent Rizzotti]

It was usual for French units coming under RAF control to take RAF squadron numbers, and using it in British documents, while keeping their own French codes and still using them in the French documents.

GC II/7 "became" 326 Sqn and GC I/3 "became" 327 Sqn in December 1943. Before that they flew in North Africa and Corsica without RAF codes. But seen from the French documents, there was no change.

Both French squadrons in Bomber Command (346 and 347) were two existing french bombers units that received these numbers while moving from North Africa to England, and converting to Halifaxes.

Even the French squadrons formed in England, like 340 Sqn in November 1941, received French codes (GC IV/2 for 340 Sqn).

As for your precise example, in French forces the equivalent of the RAF Coastal Command was under control of the Navy air force (the "Aéronautique Navale") that had a very small carrier-based part and was mostly based on the ground or used seaplanes. So a French unit flying anti-U-boat patrols from Africa will be a French Navy one, but will come under operational control of the RAF, not of the Fleet Air Arm.