acting commander of the 14th Air Force and Air Defense Army, major general Vladimir Korytkov, said that six S-400 units had been activated at the air defense formation in Russia's Novosibirsk Oblast. TASS also reported that as of the end of 2015, a total of eleven Russian missile regiments were armed with S-400, and by the end of 2016 their number was expected to increase to sixteen. 2015 - Syria It was reported in November 2015 that S-400s would be deployed to Syria along with the contingent of Russian troops and other military hardware in the course of the air campaign conducted by the Russian forces in support of the Syrian government. However, those claims were refuted by Russia. On 25 November 2015 the Russian government announced it would deploy S-400s in Syria as a response to the downing of its Su-24M jet by Turkey. By the next day, deployment of S-400 air defense systems to Syria was underway. The first S-400 unit was activated at the Khmeimim Air Base in Latakia Governorate. In April and July 2017 a second S-400 unit was activated 13 km northwest of Masyaf, Hama Governorate. Although these systems are located in Syria, they are under the command of the Russian military and not the Syrian (nor Iranian) military, making the Russian government liable if used against another state (that is, its use would be considered an attack by Russia rather than Syria). On 22 May 2018 Israeli Air Force commander, Major General Amikam Norkin, reported that Israel became the first country in the world to use the F-35I Adir in combat during recent clashes with Iran in Syria. In mid-2020, several media outlets, including Turkish media, questioned the combat capability of the S-400 air defense system. In late December 2021, the Israeli Air Force flew military jets over areas protected by S-400 and Pantsir SAM in Syria and bombed Iran-backed Hezbollah militia based in Latakia. Russia operates a naval base in the port of Tartus, 85km to the south near the port of Latakia. Considering the engagement range advertised by the Russians, the S-400 could have engaged Israeli aircraft but did not. Neither Russian fighter jets nor the S-400 systems attempted to intercept the Israeli aircraft. It is widely believed that Russia and Israel have an agreement that Israel will guarantee the safety of Russian personnel and assets during its strikes on non-Russian targets