In the inter-war period the area that now belongs to Zelmer S.A. was occupied by the Field Kitchen and Military Equipment Factory “Mars” Sp. z o.o.
On April 20, 1937, after taking over the area occupied by the Field Kitchen and Military Equipment Factory “Mars” Sp. z o.o., the construction work of the H. Cegielski Machine Tool Factory, Branch Rzeszów commenced (private ownership). The State Treasury participated indirectly in the construction process through granting long-term loans.
In the autumn of 1937 the factory started its production activity. In addition to machine tools, the factory produced multi-tool turret lathes, single-spindle automatic lathes, multi-spindle automatic lathes, multi-radial drilling machines and military equipment (anti-tank guns, anti-aircraft guns, artillery support equipment).
During World War II the plant was destroyed as its three production halls were completely dismantled and all their elements and equipment, including machines, materials and raw materials, were taken away to the German Reich.