Berling did not participate in the Polish defence effort during the
Invasion of Poland in 1939. After the city of
Vilnius was occupied by the
Soviet Union under the terms of the
Molotov–Ribbentrop Pact, Berling, along with many other Polish officers, was arrested by the Soviet secret police (
NKVD). He remained in prison until 1940, first in
Starobilsk and later
Moscow, eventually agreeing to cooperate with the Soviets. The sentence was vacated by General
Kazimierz Sosnkowski, the Polish commander-in-chief of forces loyal to the
London government in exile. , 1947 From 1940, Berling had been involved in efforts to create a Polish division in the Soviet Union, at first within the Soviet
Red Army. In September 1942 and during the following months, he and
Wanda Wasilewska appealed to
Joseph Stalin for permission to establish the Polish division. On 8 April 1943, Berling proposed the establishment of a new Polish army; permission was granted after the break in Soviet-Polish diplomatic relations. In May 1943, the
communist-led
Polish People's Army was created in the Soviet Union. It was a new formation of the
Polish Armed Forces in the East. Berling was nominated to be the commander of its first unit, the
1st Tadeusz Kościuszko Infantry Division, and was promoted to general by Stalin. He was transferred to the
War Academy in Moscow, where he remained until his return to Poland in 1947. In Poland, Berling organized and directed the
Świerczewski General Staff Academy. He retired from the military in 1953. ==Government career==