The Pak36 was a German Anti-Tank weapon that fired a 3.7cm shell. The Pak 36, being a small-calibre weapon, was outdated by the May 1940 Western Campaign, and crews found them all but useless against heavy allied tanks like the British Mk.II Matilda and the French Char B1 and Somua S35.
This 3.7 cm Pak 36 was on display at the Imperial War Museum in Duxford.
I believe that this 15mm model is an old SDD Miniatures model. It has had a white undercoat.