37 (Polish for "observers aviation rifle pattern 1937") is an aerial machine gun, a development of the ręczny karabin maszynowy wz.

It was designed as a manually operated machine gun for defensive firing positions on board combat aircraft of Polish Military Aviation.

In the mid-1930s, Polish small arms designer Wawrzyniec Lewandowski was given the task of developing a flexible gun based on the rkm wz.

The desired changes included raising the cyclical rate of fire to 1100 rds/min, replacing the buttstock with a spade grip at the rear of receiver, moving the main spring under barrel and, most importantly, changing the feed system.

This machine gun was also intended as a standard on-board weapon for other aircraft that did not manage to enter service before the outbreak of the war (PZL.46 Sum, PZL.48 Lampart, PZL.49 Miś).