I believe . . .
15 cm Schweres Infanteriegeschütz 33 (Sf) auf Panzerkampfwagen 38(t) Ausf. H (Sd.Kfz. 138/1).
I knew it as the "Bison 38H", but it took me a bit of googling to get a proper name for it. Blooz, you probably have a picture of the M version in which the engine was moved forward and the gun mounted on the back. But the H version still had the engine to the rear and short-barreled gun placed forward.