The exact caliber is somewhat uncertain. Officially, it was 10 cm, but in the German designation system this typically meant 10.5 cm (105mm). The basis for the caliber and ammunition would likely have been the 10 cm "Nebelwerfer" 35, a mortar of 105mm caliber used in small numbers by mountain troops. The gun carriage for the prototypes was that of the 5 cm Pak 38 or the "Sonderlafette" V1. Both were only waist-high and would have easily been sited and camouflaged well within their maximum effective range. The PAW was a very special development that enabled low-cost guns on old carriages to defeat the most modern tanks of World War II. Its maximum effective range was surpassed by classic anti-tank guns due to its rather low muzzle velocity, but the non-spinning shaped-charge shells offered effective anti-tank capability at ranges that exceeded the envelope of portable weapons. In 1944-45, the Germans changed their system of artillery designations from the old "year" system. Each weapon was to have a number showing its caliber group, a letter denoting the ammunition group, and the last two digits were from the weapon drawing number. In this case, 10 denoted 100 mm caliber using the H group of ammunition.