S-125 PECHORA MISSILE CONTAINER TANKS
The missiles are stored in a protective atmosphere before being prepared for use. The protective atmosphere is made of nitrogen, the same element used as the gas operating the guidance fins and some other equipment on board the missile. This was to save equipment: The same compressor and gas generator could be used for storing and preparing the missiles for use. Nitrogen also prevents water from entering the stored missile and therefore corrosion from happening.