Need some help determining what the officers uniform signifies. It was taken at the post de secours at Hüss in Alsace in May-June 1915.

If anyone is interested I found out.  He is a lieutenant in the 11e chasseurs à cheval.  

(11e régiment de chasseurs à cheval) A cavalry regiment dating back to Napoleon.  From Wikipedia - 

World War One

On 31 July 1914, the regiment assigned to the 7 th  army corps , mobilized [ 5 ] . A squadron group is assigned to the 14 e DI in Belfort and the other to the 41 e DI in Remiremont [ 6 ] .

Since the August 4 , 1914  is in contact with the enemy in Alsace . The regiment's cavalry were the first to enter occupied Mulhouse [ 6 ] , [ 7 ] . At the end of August, the various squadrons joined the Somme [ 8 ] to try to stop the Germans, in vain until the Battle of the Marne [ 4 ] .

 

In 1915, while the war is gradually becoming a trench warfare , the 11 th  fighters regrouped tries to climb attack Saint-Hilaire-le-Grand onSeptember 25, 1915in an attempt to outflank the front. The five charges are repulsed but the regiment is cited to the order of the army [ 4 ] , [ 9 ] .

 

In 1916 ,  fought on foot in Verdun and in the Somme [ 4 ] , [ 10 ] . In 1917 , squads regiment, each associated with a division involved in the offensive Chemin des Dames , the 1 st  squadron with 14 e  DI, the 2 e with 128 e  DI , the 3 e with 41 e  DI and 4 th to 164 th  DI [11 ] . In 1918, fighting partly on foot and partly on horseback, the regiment faced theGerman Spring Offensive . The 18th July 1918, the German front is pierced by the French [ 4 ] . The regiment received in 1919 its second citation to the order of the army following these battles [ 12 ] .

je ne pourrais pas aider sur ce sujet