As the Second World War progressed, the need for ever increasingly more powerful anti-tank guns would evolve; to counter ever more powerful and better armed Tanks and AFVs among other things. With the Russians fielding increasingly more powerful guns such as the 122 mm, and tanks such as the IS-2, the need for what would become the PaK 44 became apparent. The guns initial requirements were made in 1943. The PaK 44 would have the capacity to act as a field gun, firing HE rounds and also act as an anti-tank gun.
The production model was a Krupp design; see blow:
A version was under development by Rheinmetall Borsig but ultimately it was dropped; see below: