British 2" Mortar
The soldiers are wearing British 44 pattern Helmets
The shoulder flash I think indicates from the IV British Corps.
Oh yes I even have a picture of that aiming device in use, its lined along the barrel and shows the angle its is laid at.
Based on a Spanish design, into production in 1938, out of service in 1970. Can be fired horizontally.
This pic is one of 3 variations (mainly to do with the gound mount).