Like in title, old, pre-war firefighters' engine. Not any exact model, just a "generic" one, loosely based on multiple photos I've looked at. Scale is too big for minifigs and too small for technic figs, so the model is unmanned for now.
A word about durability: Model can be considered as medium-resistant, 2-levelled, with only internal strenghtened. It means that in collision details will detach but internal structure will remain undamaged.