French Adrian Helmet Model 26.
This helmet was completed with a reproduction liner.
If you are interessted in a lot of detail see: world war helmets Casque Francais Adrian Mle 26
This is a big helmet, at the inside you can see a "D", this shel is suitable for liner sizes 60-62.
The large ventilation hole under the comb, which had been a weak point of the old M15 design, was replaced with a series of small holes.
The comb of this helmet is made of aluminum. Based on this and shape of the comb the manufacturer of this helmet could have been: Dunois or Japy, I have a feeling it is made by Dunois.