The 210 mm gun M1939 () was a Czechoslovak

Czechoslovakia

Czechoslovakia or Czecho-Slovakia was a sovereign state in Central Europe which existed from October 1918, when it declared its independence from the Austro-Hungarian Empire, until 1992...

 heavy siege gun used by the Soviet Union

Soviet Union

The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....

 during World War II

World War II

World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

. After the Germans occupied Czechoslovakia in March 1939 they took over the Škoda Works

Škoda Works

Škoda Works was the largest industrial enterprise in Austro-Hungary and later in Czechoslovakia, one of its successor states. It was also one of the largest industrial conglomerates in Europe in the 20th century...

, which had been working on this design and a companion 305 mm howitzer. As a result of the Molotov-Ribbentrop Pact

Molotov-Ribbentrop Pact

The Molotov–Ribbentrop Pact, named after the Soviet foreign minister Vyacheslav Molotov and the German foreign minister Joachim von Ribbentrop, was an agreement officially titled the Treaty of Non-Aggression between Germany and the Soviet Union and signed in Moscow in the late hours of 23 August 1939...

 the Germans sold both designs to the Soviet Union. It's not entirely clear that Škoda actually built the weapons itself or merely supplied the blueprints. At any rate, very few weapons seem to have built, so much so that there's no record of the Germans capturing any after Operation Barbarossa

Operation Barbarossa

Operation Barbarossa was the code name for Germany's invasion of the Soviet Union during World War II that began on 22 June 1941. Over 4.5 million troops of the Axis powers invaded the USSR along a front., the largest invasion in the history of warfare...

.

It used the same carriage as 305 mm howitzer M1939 (Br-18)

305 mm howitzer M1939 (Br-18)

The 305 mm howitzer M1939 was a Czech superheavy siege howitzer used by the Soviet Union during World War II. After the Germans occupied Czechoslovakia in March 1939 they took over the Skoda Works, which had been working on this design and a companion 210 mm gun. As a result of the...

as well as the same firing platform and control mechanism. It was transported in three loads.