Complex sentence: It was the GC3 ("Groupe de Chasse 3" or 3rd Fighter Group) in the Free French Air Force, first commanded by Jean Tulasne (the's' is silent).
Split into simpler sentences: It was the GC3 ("Groupe de Chasse 3" or 3rd Fighter Group) in the Free French Air Force. First commander was Jean Tulasne (the's' is silent).