Steel breastplate, or Stalnoi Nagrudnik (Russian: Стальной нагрудник) is a type of body armor similar to a cuirass developed by the Red Army in World War II. 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 2mm and weighed 3.5kg (07.7lb). This armor was supplied to SHISBr (assault engineers).
Several models were created; the number indicates the year of development:
The steel breastplates along with the conventional steel SSh-40 helmets equipped the assault engineers and demining brigades of the Supreme Command Reserve Stavka, for which they are sometimes called "tubular infantry." Breastplate SN-42 was designed to protect against bayonet attacks, small fragments of shrapnel, and 9mm pistol bullets with lead cores, providing protection against fire from an MP-38/40 submachine gun from close range, but were useless against rifle rounds such as 7.92×57mm Mauser. Following the adoption of the Wehrmacht on the supply of 9mm cartridges, the cartridge code R.08 mE (German: mit Eisenkern), with a bullet with mild steel (iron) core, required the thickness to be increased to 2.6mm for the chest plate (2.5mm2.7mm). This redesign received the name SN-46.
By modern standards, they are roughly equivalent to a Class II vest.
Estimates of the plates' performance from front-line soldiers were mixed, receiving both positive and negative feedback. The vest worked well in street fighting and other types of close quarter combat. However, in the field where assault teams often had to crawl the breastplates were just an unnecessary burden.