Upon its introduction to service, it was popularly considered to be not only the most modern and effective weapon then possessed by Poland, but also to be one of the most advanced bombers then operational in the world. On 1 September 1939, the Polish Air Force had roughly 86 PZL.37s in total, but less than a half of those actually saw active combat use due to aircraft being used by training units, being in maintenance, or having been held in reserve. The bombers suffered from a high attrition rate due to lack of fighter protection, and the final Polish combat missions were performed on 19 September. During October 1940, around 26-27 of the PZL.37s that had been evacuated from Poland were seized by the Romanian government and 23 of these aircraft were subsequently used by the Royal Romanian Air Force, including offensive missions against the Soviet Union.