Newsweek writes about it.
According to the International Institute for Strategic Studies, in early 2023, Russia had about 100 S-400 mobile air defence systems.
According to analysts at the Dutch intelligence service Oryx, Russia has lost key components of its S-400 batteries at least five times, including command posts, launchers, and radars. Other losses of S-400 stockpiles are possible, and some reports indicate an unspecified number of damaged systems.
The S-400 is generally considered to be the equivalent of the US Patriot air defence system and the gold standard of Russian air defence. It is an upgraded version of the Cold War-era S-300, which is still in use today.
Experts say that the S-400 is increasingly becoming the target of Ukrainian attacks, which it has not been able to repel. The loss of an S-400 system, while still relatively rare, is a painful, costly and humiliating blow to Russia's air defences. Each S-400 battery costs about $200 million, according to Sidharth Kaushal of the Royal United Services Institute, a London-based think tank.
Two of Russia's reported losses occurred in the last 30 days. On 14 September, Ukrainian forces struck the S-400 near Yevpatoriya, on the Russian-controlled Crimean peninsula. The drones first attacked the radar and antennas, and then missiles destroyed the rest of the S-400 system.
Kyiv also targeted another S-400 system in western Crimea on 23 August, in an attack that a Ukrainian official said was carried out by a "new, absolutely modern" missile. This is believed to hint at a land-based version of Ukraine's Neptune anti-ship missiles.
It is worth noting that before the war in Ukraine began in February 2022, Russia had five S-400 batteries in Crimea, and two of them have already been disabled.
The loss of the S-400 has made Russian targets in Crimea more vulnerable to attacks by Ukrainian Storm Shadow cruise missiles, said military expert David Hambling.
"On September 13, Ukraine damaged a Russian warship and submarine docked at Russia's Black Sea naval base at Sevastopol, with what are understood to be Storm Shadow missiles. Satellite images shared with Newsweek then showed the aftermath of the strikes on the Crimean dry dock".
"We may now be seeing the start of a trend where S-400s are increasingly targeted," Hambling said. However, Russia is likely working to strengthen the defences around its S-400s, the expert suggested. "This type of conflict tends to be a battle of successive improvements on both sides," he argued.
The S-400 is Russia's "premium" air defence system, but according to Hambling, Russia's loss of several S-400s in recent months is significant for several reasons:
The first is that the S-400 "appeared to have performed well previously but now appears vulnerable," he told Newsweek.
"Secondly, knocking out S-400s punched holes in the air defense network that are then exploited," Hambling added.
The S-400 is linked to other Russian systems, such as the Buk, which means that if the S-400 is hit, it will "disrupt the functionality of local air defence systems as a whole," Kaushal said.
"The S-400s have performed nominally," commented Ian Williams, deputy director of the Missile Defense Project at the Center for Strategic and International Studies.