Under his influence, the yeshiva joined the musar movement definitively and Rabbi Zalman Dolinsky of Radun was appointed as its first mashgiach (spiritual supervisor).

By the time World War II broke out there was hardly a rosh yeshiva of the Lithuanian school who had not studied in Mir.

The invasion of Poland in 1939 by Nazi Germany from the west and the Red Army from the east meant the yeshiva was unable to remain in Mir, which was now under Soviet control.

While many foreign-born students left, the majority of the yeshiva relocated to Lithuania, which had been occupied by the Soviet Union but not yet fully absorbed.

It was obvious, however, that this arrangement was only a temporary solution, and that ultimately the yeshivah would need to flee Soviet-occupied Lithuania in order to survive.

Concurrently, it became known that the Japanese consul in Lithuania, Chiune Sugihara, had agreed to issue transit visas to refugees who wished to escape via the Japanese-occupied Pacific.

As a result, most of the yeshivah students requested and received several thousand transit-visas from Sugihara, permitting them to depart to the Far East.

In the fall of 1940, the yeshiva students traveled via the Trans-Siberian Railway to Vladivostok, Russia; and then by ship to Tsuruga, Japan.

[4] In America, he established the Mirrer Yeshiva Central Institute in Rockaway and later moved it to Brooklyn, New York City.