Sorry for my late answer, ROLAND1369ROLAND1369 wrote
My best guess would be French 240 MM Mortier LT Mle 1916
I think you are wrong. I think there are some differences. The carriage shape it not identical and the handwheel is different respect to the French 240mm Mortier LT Mle 1916.....
Othe countries copied this model: US, Great Britain, Italy, Germany and Austro-Hungary, but all of them seems identical copies to the French model....
Regards
Sturm78