The PZL.37 Łoś (English: elk) was a modern Polish twin-engine medium bomber, used in the defense of Poland against the Nazi German Invasion in 1939. It is sometimes known as "PZL P-37" or "PZL P.37", but the letter "P" was generally reserved for fighters of Zygmunt Pulawski's design (such as the PZL P.11). The correct designation should be PZL.37.
Before the war, the PZL.37B Łoś was one of the world's most modern bombers. It was able to carry a heavier bombload than similar aircraft, for example the Vickers Wellington, though the size of the bombs was limited. Smaller than most contemporary medium bombers, it was relatively fast and easy to handle. Thanks to a landing gear with double wheels it could operate from rough fields or meadows. Typically for the late 1930s, its defensive armament consisted of only 3 machine guns, which proved too weak against enemy fighters.