The mystery howitzer you are looking for is a Soviet 152mm (Model 1909-30 Schneider?) howitzer (according to the sign in front of it 1944).
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Iran didn't have any German weapons pre-1945, except WW1 MG08, Lugers (via Switzerland) and C96 Mauser pistols (pre-WW1). The purchased artillery pre-1945 was entirely Skoda and Bofors. The early Artillery were left-over Ottoman, Russian and British