What has been Russia's response to the US strikes on Syria?

Question

Russia warned of consequences for the strikes against Syria, and it seems they have made warnings prior to the strikes.

Has there been a response or a mobilization of their military that might indicate retaliation?

Answer 1

Good question, though it's not popular to answer these type of questions because people perceive any answer is defending a side, even if we're trying to look at the situation objectively. Mobilization of military or response may happen in other contexts - mobilization of a cyber military or economic response.

The answer depends on how you see the response or lack thereof so far:

• Russia has done nothing direct other than sell some of its equipment to Syria, as the other answer notes along with some training of its military alongside China, which happened very close to the Syria attacks. The people who want to believe that Russia has done nothing, will accept this as the correct answer.
• Russia may act indirectly, which is something we wouldn't know, such as a cyber attack. Also, it may not be a cyber attack against the US, but against another country, such as an ally. Economic acts behind the scene that we don't see directly could also have Russian involvement (Turkey repatriating its gold right after the Syria attack - may or may not be indirectly related; Chinese investors looking at investing in Rusal if there's special negotiations in their favor).
• Russia may do nothing at all indirectly or directly more than what's done because they may weigh their options as unfavorable, whether US military power being a reason or a better strategy being a reason. If Russia knows they can't fight the US, they won't respond overtly and they may be careful about covert action. If they know they can respond, but it's not the "moment" to do so, they may wait for the right time.

People will see what they want to see in this answer.

Answer 2

Russia decided to transfer S-300 surface to air missile (SAM) systems to the Syrian Arabic Republic (SAR).

No western sources for now, only russian: https://www.gazeta.ru/army/news/2018/04/23/11446483.shtml (one of)

This will greatly improve SAR defence systems. Existing SAR middle-range systems are rather old: S-75 and S-125 in most, and some S-200. These are rather good systems: S-75 used in vietnam war and cause notable casualties to US air forces, one of S-200 downed F-117 while Balcan war.

They also show good results in defending last strikes, but their possibilities are shortened comparing to modern systems. They can strike only one target at a time, while S-300 can strike to six.

Also it can be noted, that S-300 is more applicable for striking down hard and fast targets - jets for example. Using it for blocking tomahawks strike is just overkill. Maybe this is some preparations for US carrier strike group arriving.

Answer 3

Has there been a response or a mobilization of their military that might indicate retaliation?

No.

Russia has stated that the U.S. conferred with it and did not cross Russia's "red lines", effectively ratifying the U.S. action while not actually approving of it. The Washington Post reports that:

Russia’s foreign minister said Friday that the U.S. sought out and respected Moscow’s positions in Syria when it launched its air strikes last week.

Lavrov noted that despite the escalating tensions between Moscow and Washington, the U.S. made sure it didn’t harm any Russian personnel and positions during the strikes against the regime of President Bashar Assad following a suspected chemical attack on the town of Douma.

“We told them where our red lines were, including the geographical red lines,” Lavrov told Russian state television. “The results have shown that they haven’t crossed those lines.”

Russia did not respond during the strike with its advanced air defense systems on the ground in Syria.

Russia did apparently decide to sell Russian S-300 surface to air missiles to Assad's regime, (although not its more sophisticated S-400 systems), after previous equivocating purportedly in the face of Western opposition to the sale.

The S-300 sale is potentially a threat to intervention by air in the Syrian Civil War by the U.S. or its allies (the U.K. and France, for example, also participated in the chemical weapons retaliation strike in April of 2018, and Turkish aircraft have intervened in parts of the Syrian Civil War as well, for example, shooting down a Russian jet fighter which was intruding into its air space). But, this was, in part, a response to the general situation which was being contemplated even before the latest U.S. allied strike related to chemical weapons usage.