The Munitionpanzer IV was an altered version of the
versatile and ubiquitous Pzkpfw IV to transport ammunition for the
siege howitzer Karl. It carried and helped reload the gigiantic shells
for the Karl.
The Munitionsfahrzeug III/IV was used to re-supply the
self-propelled artillery Hummel. It was much needed because each Hummel
could only carry 18 rounds.