The two largest ships of the Russian Navy, the nuclear powered  battlecruiser Pyotr Velikiy (099) and the aircraft carrier 'Admiral Kuznetsov' (063) are now in the English Channel, steaming toward the eastern Mediterranean. Their mission is to establish a 1,500 km naval exclusion zone outside the coast of Syria and to sink any US carrier strike group willing to challenge them. 

NATO says the 'Kuznetsov' is on a mission to “bomb rebels in Aleppo”. This is true only as much that this is a combat mission; not a summer cruise, a training exercise, or just showing the flag. In fact, this is the first time any Russian or Soviet aircraft carrier has seen combat. 

Quote: "Russian warships off the coast of Norway are carrying fighter bombers that will likely reinforce a final assault on the besieged Syrian city of Aleppo in two weeks, a senior NATO diplomat said on Wednesday citing Western intelligence," reports Reuters.

The Russian battle group, once it is assembled in the Mediterranean may be the largest European naval formation to see combat since the Battle of Jutland in 1916. Wikipedia

Most likely the battle group will include several nuclear attack submarines, of the 'Akula' and 'Oscar' classes. Wikipedia

Their mission is to stop the planned American war on Syria and to prevent the US Navy from launching airstrikes or  Tomahawk cruise missiles at the Syrian Arab Army or the Russian forces in Syria. This is a repetition of the situation in August 2013, this time with an even larger Russian naval presence.

Soviet capital ships were designed to sink American aircraft carriers. Their main weapon is the P-700 Granit supersonic anti-ship missiles carried on the 'Pyotr Velikiy', the 'Kuznetsov', and the 'Oscar' class submarines. Wikipedia

If the Russian force is threated, they will be supplemented by 'Tupolev Tu-22M' strategic bombers carrying 'Kh-15 and Kh-32' anti-ship missiles with operational ranges of 300 km and 1,000 km respectively. The bombers may be deployed to Syria or the Hamadan Air Base in Iran. 

The US is now openly preparing for war against Syria. Their previous attempt in August 2013 failed because of the Russian naval presence outside Syria. The events were mostly kept secret from the Western audience. 

The standoff was first described by Israel Shamir in October 2013: “The most dramatic event of September 2013 was the high-noon stand-off near the Levantine shore, with five US destroyers pointing their Tomahawks towards Damascus and facing them - the Russian flotilla of eleven ships led by the carrier-killer Missile Cruiser Moskva and supported by Chinese warships.

Apparently, two missiles were launched towards the Syrian coast, and both failed to reach their destination.” 
The Cape of Good Hope.

A longer description was published by Australianvoice in 2015: “So why didn’t the US and France attack Syria? It seems obvious that the Russians and Chinese simply explained that an attack on Syria by US and French forces would be met by a Russian/Chinese attack on US and French warships. Obama wisely decided not to start WW III in September 2013.” Can Russia Block Regime Change In Syria Again? Link to source.

In my own comments from 2013 I tried to understand the mission of the Russian fleet. This is what I believed Putin's orders to the fleet were:

1) To sink any NATO ship involved in illegal aggression against Syria.
2) You have the authority to use tactical nuclear weapons in self-defense.

I am sure NATO admirals understood the situation the same way.  I am not sure of the American leadership in Washington.

Petri Krohn, editorial article