This is a well-made, tailored Modèle 1915 bleu horizon tunic of the Aeronautique Militaire complete with aviation winged star Pattes De Collet collar insignia, loops to hold an aviator's brevet over the right breast, and a matching set of French grenadier buttons marked “H.J. Paris," suggesting that this was the pilot's original service.  The tailor was "Cook & Co, 23 Rue Auber - Paris" and his label is marked "Seinelaigue" and dated "17.10.1917." The pilot who wore this tunic was a Sergent as designated by the gold chevron above each cuff which are the later, reduced version of the much larger chevrons worn earlier in the war.  The insignia on the collar tabs measure 44 mm in length (see Bartlett, page 345). Note that the collar insignia are reversed and head outwards instead of inwards indicating that the collar - typically because of fraying from wear - was flipped, as illustrated in the 2nd photo below.  The 3rd photo is from the 16 Septembre 1917 issue of La Guerre Aérienne Illustrée which celebrated the brothers Lucien & Leon Coupet, "Deux As Bombardiers: Les Frères Coupet;" note that Lucien's insignia is similarly facing outwards instead of inwards, as with this tunic.  The brevet in the opening photo is not part of this tunic.