Looks v. much like a gun used to trigger avalanches before they go critical at unwanted times - and, in the fall-back mode, for hurling thermos canisters of gluhwein up onto the higher slopes for the thirsty and adventurous.
We can ignore the strapwork as this is just to hold it to the rock.
Large F*off clamping handle to RHS and flange so it's unlikely to be a field/infantry weapon such a mortar or kreigspistolle. Reminds me of the 1.5" very pistol.. Cant throw much as the breech does not look that strong?
What's confusing me is the pipe fitting on the left hand side of the breech...
WTF is that for? It looks like it is draining rain from the barrel - so it may be a later additon - but why not just drill a hole?
My guess it is either an AFV mounted discharger as Old_bloke says or it could be a fortress mounting for covering a door or a tunnel entrance?
On the other hand the pipe fittings look Naval to me...
Things like this annoy me, they really do! I just tried to post this on "forum-militaria", the (sort of) Wop equivalent to ARRSE. However, I got the message: "Spiacenti ma il forum al momento non e disponible, prova piu tardi". Which means the site's down at the moment and to try again later.
I reckon that's gonna be our best bet, because them boyos really know their onions and if anybody can identify this piece of kit, it'll be them. I'll give it another cabby later on.