There were several models of body armour in the Red Army, called SN-38, SN-39, SN-40, SN-40A, and SN-42. The number denotes the design year. All were combat tested, but only the SN-42 ("Stalynoi Nagrudnik" is Russian for "steel bib") was put in production. (The native Cyrillic abbreviation for the vest was СН, the Cyrillic letters Es and En.)
It consisted of two pressed steel plates that protected the front torso and groin. The plates were 2 mm (.08") and weighed 3.5 kg (7.7 lbs). This armour was supplied to SHISBr (assault engineers) and Tankodesantniki (infantry that rode on tanks) of some tank brigades.
Real combat experience showed that the MP-40 9 mm bullet failed to penetrate at around 100-125 m (100-130 yards). It was very useful in dense, intense urban battles (Stalingrad) where the Germans used the MP-40 predominantly, but, because of its weight, was not practical for soldiers charging across an open field.