Looking through archival videos, I recently caught a glimpse of a very strange grenade launcher, only visible for a few seconds. I compiled footage from the original video:
Searching on websites, books and photo collections did not help. In WWI there were several similar grenade launchers, which mostly fired flare grenades or canisters containing small notes for safe communication with neighboring units. But I have never before seen a grenade launcher with a rifle stock and a sideways barrel.
There is a clue that it could have been a pre-war police grenade launcher for throwing smoke and tear grenades, especially since the video shows the launcher with two different grenades. The presence of a French officer in the video gives a clue that the weapons are also of French origin. Similar grenade launchers produced from converted old rifles were used in the armies of many countries: including France, Belgium and Germany.
If someone knows more about this thing, then please share the information.