The S-400 surface to air missile (SAM) system is one of Russia’s most important assets in Syria, as well as in Eastern Europe where the system’s presence in the Russian enclave of Kaliningrad gives the Kremlin powerful airspace denial options over the Baltic States and much of Poland. The S-400 system consists of wheeled vehicles including long-range surveillance radars, tracking and engagement radars, missile transportation and launch vehicles, and a command and control node.
https://rusi.org/publication/rusi-defence-systems/russia%E2%80%99s-air-defence-challenge-syria
https://day.kyiv.ua/ru/blog/politika/donbass-ruchka-dlya-chemodana
https://focus.ua/country/375470/
https://focus.ua/country/375464/
https://www.gazeta.ru/politics/2017/06/29_a_10754015.shtml
https://ru.krymr.com/a/28585941.html
https://ru.krymr.com/a/28585372.html
http://www.kasparov.ru/material.php?id=59552F6D92CBF