Unlike Great Britain and Germany, the French military never developed a formal sniper doctrine during World War One - they had no dedicated schools or instruction manuals for that specialty. The three major arsenals did produce scoped sniping rifles, however, with models of 1915, 1916, and 1917 (and a post-war 1921 pattern). We have a model 1916 example here today.
The rifles were completely ordinary off-the-rack Lebels, modified simply to add scope mounts. The 1916 pattern mount used a round peg on the side of the rear sight and a bracket wrapped around the front of the receiver, which allowed the scope to be quickly and easily detached for carry in a separate pouch (similar to what other nations did, to protect the optic from damage when not in use). The rifles were issued only in small numbers (2 per company, or even 2 per battalion) and it was left to the unit commander to decide how to employ them.
This particular scope has some neat provenance of being brought home by a US soldier after the war - it came back wrapped in a period copy of Stars and Stripes magazine. The rifle is of the appropriate type, but the “N” marks on the barrel and receiver indicated French overhaul in the 1930s, precluding it from being the original rifle this scope was mounted on.
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