Main production run of PZL 37 - differed from 37a in having twin fins and formed main body of Polish Air Force bomber arm. Those that survived the German invasion (many being destroyed in combat, captured by the Germans or destroyed by the Poles to prevent them falling into enemy hands) flew to Romania. Initially the Romanians used them as trainers but they were used operationally against the Soviet Union when they assisted the Germans in the invasion of Russia.