The Soviet D-44 Divisional Gun can trace its origin to the German Flak 88mm Anti-Aircraft cannon of WWII notoriety.
During the Spanish Civil War in 1936, the Soviet Union observed the German Flak 88 in use by Republican Forces and developed the 85mm M39 Anti-Aircraft gun based on the German Flak.
The projectiles when placed side by side are virtual identical.
Like most anti-aircraft guns, it was discovered the high velocity 85mm cannon was also effective as anti-tank gun and in late WWII became the T34/85 tank gun where it was a very potent weapon against the heavily armored German Tiger tanks which were likewise equipped with a version of the Flak 88.
The Germans also mounted the 88mm cannon on an improvised carriage as the Pak 43 anti-tank gun. It was nicknamed the "Barn Door" because it was heavy and unwieldy due to its 8000 # weight.
It was however still very effective.
The Soviet Union observing the effectiveness of the German Pak, and its shortcomings, designed an entirely new anti-tank gun in late WWII based on their 85mm cannon. Light weight, narrow and low height, it was designated the D-44 Divisional Gun which meant in addition to anti-tank munitions, it could also fire HE rounds to extreme ranges.
After WWII, the SU-85 self propelled tank destroyer was another iteration of the same cannon.
The D44 was used in the Korean War, the Vietnam War, and virtually every war or conflict in the Middle East. They are still present in North Korea and most former Soviet allied countries.
Not surprisingly, the D44 has been observed in Ukraine.
