Over 100 were produced by the outbreak of World War II, the last few being the first aircraft manufactured at the new Mielec plant in southern Poland. Only 36 Łoś' were in active bomber units before the Invasion of Poland. A further 18 were in reserve at the Małaszewicze base and a dozen in training. The remainder of the aircraft was being finished slowly at the PZL factories in Warsaw and Mielec, with the main emphasis shifting to the production of fighters. During that time Dąbrowski designed a very promising low-wing fighter with inline engine, PZL.62, but the war prevented its development. During the World War II Dąbrowski was evacuated to Romania and then to England where he was a technical officer with the Polish Air Force. After the war ended he completed his degree, worked at Percival Aircraft and Folland Aviation. In 1955 he moved to the United States working initially at the Cessna Aircraft Co., then Stanley Aviation and finally Boeing where he specialized in advanced studies. He died while working in Renton, Washington on September 17, 1967. Jerzy B. Cynk (1990): "Samolot bombowy PZL-37 Łoś", Wydawnictwo Komunikacji i Łączności