After the Soviet Union declared war on Poland in the last days of 1938, the Poles flew the PZL.37 against Russian cities, Army positions, and air fields. Soviet pilot Sergei Yaroslavsky was envious of the bombers - which they nickednamed Elk's - ability to carry twice the bomb load of his own SB-2, but was grateful that the Pol's lacked the numbers for the bomber to be a true threat. After Germany entered the war on the Pol's side, the PZL.37's made two big raids on the Russian cites of Minsk, and Zhytomyr.