Thanks for the response, guys.
First, let me give you an idea of its size. The total length is 55 cm. It's quite a big knife. The width is about 5 to 6 cm (that's a guess).
It also made me think of the sidearms worn by pioneers or 'sapeurs'. The sheath is made of leather (nicely stitched) with brass metalwork. My friend, who is a collector of WW 1 items, thinks this piece has a German origin. He deduces this from the frog stud on the locket or top mount.
The crossguard has two quillons, one pointing upwards and the other one pointing downwards.
There's no way to mount it on a gun. There is no attachment bar. I think it would be too heavy for this.
Should me friend come up with something, I will surely let you know.
