There is a faded tag behind this gun but neither I nor museum’s technician can decipher it. Any guess? Something Spanish?
Looks very much like a 37mm (2lb) ,falling block,Nordenfelt gun. This single shot gun was used on small anti torpedo boats. I think the 33kg refers to the weight of the gun (approx. 72lbs).
Favored by the Spanish Navy, many of them where captured by the U.S. Navy in Cuba. There are variations with a shoulder stock. I saw one so equipt at a Maritime museum in Washington state.