«Turkey's Russian air defence systems and U.S. response». Reuters.com. 1. oktober 2021. Besøkt 3. oktober 2021. «Turkey received the first deliveries of the S-400 surface-to-air systems in July 2019, prompting Washington to begin removing the NATO ally from its F-35 stealth fighter programme over security concerns.»
Franz-Stefan Gady (3. februar 2021). «Russia Completes Delivery of Second S-400 Regiment to China». thediplomat.com. Besøkt 3. oktober 2021. «Russia has completed delivery of the second regimental set of Russian-made S-400 Triumf long-range interceptor-based air defense systems (NATO reporting name: SA-21 Growler) destined for service in the Chinese People’s Liberation Army Air Force (PLAAF), according to a Russian military diplomatic source.»
