The Panzer IV was used for many different roles.
This one is the ammo carrier for the 560mm and 600mm Mortar Karl series.
Two or three ammo carriers were assigned per mortar.
They had a crane to transfer the ammo to the mortar.
Only a small amount of ammo was moved at a time to minimize the chance of disaster in the event of attack.
Models in HO scale, made by ArsenalM. https://www.fidelismodels.com/product/ArsenalM_112100021.html