It entered service in 1936 becoming the standard grenade launcher of the Polish Army; it was still in use during the German Invasion of Poland in 1939.

[3] Work on a new weapon was resumed by the Institute of Material Research for Armament (Polish: Instytut Badań Materiałowych Uzbrojenia) by a team led by Lt. Col.

[3] After a series of successful tests, the weapon was accepted by the Polish Army under the designation of granatnik wz.

[3] Meanwhile, the Instytut Techniczny Uzbrojenia (Armament Technical Institute) continued to improve the design and eventually came up with four different projects, initially code-named "type A", B, C and D.[4] (some sources call them "granatnik wz.

[5][3] The Centre for Ballistic Studies at Zielonka conducted extensive tests of the four new prototypes hand-made by the Warsaw-based Państwowa Fabryka Karabinów.

Unlike ordinary mortars of the era, the firing angle was fixed at 45 degrees and the range was regulated not by raising or lowering the barrel but by limiting the volume of a gas chamber (see also the Type 89 grenade discharger).

The unrifled 46 mm barrel was attached to a flat base equipped with a bubble level and stabilised by a folding bipod.

By turning the valve, soldiers operating the mortar could limit the size of combustion chamber beneath the grenade, setting the muzzle velocity and thus the firing range at between 100 and 800 metres (700 for the wz.

[7] However, due to the complexity of the design, field repairs were significantly more difficult than with conventional mortars.