One month ago we reported that Russia had deployed S-400 air defense missile systems in proximity to Moscow, which were then put on combat duty. “The SAM combat squads of the Moscow Region aerospace forces have put the new S-400 Triumph air defense missile system into service, and have gone on combat duty for the air defense of Moscow and the central industrial region of Russia,” the Defense Ministry’s Department of Information and Mass Communication told Interfax in early January.

While the ministry did not explicitly state why the rollout was taking place, it added that “the main task of the anti-aircraft missile troops of the Russian Aerospace Forces is air defense and protecting vital state, military, industry and energy facilities, as well as the Armed Forces troops and transport communications, from aerospace attacks.”

Fast forward one month, when overnight the missile systems in proximity to Moscow got their first real test, when air defense systems around Moscow were put on high alert Wednesday as part of a surprise nationwide combat readiness drill for the Russian Air Force which was meant to "test how prepared Russia is to repel a possible attack.“

“Units of the air defense force responsible for defending Moscow and the central industrial region have been put on highest combat alert,” the Russian Defense Ministry said in a statement. “The air defense mission involves fully-manned combat crews.”

A part of the test, the ministry added, involved the redeployment of batteries of S-300, S-400 and Pantsir-S air defense systems to backup positions in a simulation of area contamination. The guards of the batteries also conducted anti-saboteur maneuvers and trained to operate in hard terrain.

Russia Deputy Defense Minister Aleksandr Fomin said that the drill is part of the surprise Russian Air Force training ordered by President Vladimir Putin on Tuesday. It involves 45,000 troops and 1,700 pieces of military equipment, including 150 aircraft and 200 surface-to-air missile launchers. Fomin met foreign military attaches on Wednesday to brief them on the situation.

“This is a surprise exercise and thus not subject to control under the Vienna document or the OSCE documents. No formal notification was required, but we do inform you as a gesture of goodwill,” he said. The snap exercise will last until Thursday, Fomin added. The Russian official said it is meant to test how prepared Russia is to repel a possible attack.“

"During the test we pay special attention to the deployment of air defense and the readiness of aviation groups to respond to an aggression,” he said, before detailing how exactly Russia was moving its troops during the exercise.

As RT adds, the briefing came amid alarmed reports in some Western media outlets which claimed that the exercise was meant to telegraph Russian preparations for war.