If the troops were German, and from the weapon description, it sounds more like the Bergmann or the Schmeisser made version thereof. The box magazine version. The version with the snail drum mag was issued to the stormtroopers of WWI. After the mp38 was issued to the army, the Bergmanns were phased out from frontline use and many of them were issued to Polizei/anti partisan formations. There are photos of polizei troops using them during the Warsaw uprising. A lot of confusion arises from the fact that Allied material constantly identified the mp 38 and mp40 as a schmeisser, when in fact they were designed and made by ERMA, The key differences being the absence of a wooden stock, replaced by a folding metal stock, and the increased use of stamped metal parts. Although the mp 38 had Bakelite grips on the pistol grip, these were phased out with the mp40. It sounds as if the picture was too early to be the fg42 or even a sten.