Polsten is a British Anti-air unit.
Polsten was a Polish version of a a simplified Oerlikon cannon. The Polsten was cheaper costing between £60 and £70 over the Oerlikon £320 due to the reduced number of components, 119 of the Polsten over to 250 of the Oerlikon.
These were supposed to be issued to various front line units for example the Motor Battalion's Signals Platoon had two while the Admin Platoon had four. In real life, front line units never used it in large numbers with only the Divisional LAA Regiment having Light AA Troop of eight 20mm guns in each battery.