An expert told Forces News the aircraft carrier can, at the very least, expect to be monitored by the Chinese as Beijing will not wish to appear 'bullied' by foreign forces.
China's warnings have so far been all words rather than action, but the waters remain hotly contested.
So too are the small islands and reefs they contain, claimed by several neighbouring countries, and China is becoming increasingly assertive.
Beijing has laid claim to the majority of the area – it has even set its own boundaries.
But the rest of the world does not recognise them.
Watch: US Defense Secretary talks up UK-led Carrier Strike Group as HMS Defender visits Brunei.
Beijing is angry following US Freedom of Navigation operations – America uses surveillance flights to keep a routine watch over the region.
Asia-Pacific expert at RUSI, Veerle Nouwens told Forces News: "The Chinese have had some close encounters with, for example, American vessels.
"There have been some accusations of unprofessional shadowing at too close ranges. That, of course, can lead to unintended accidents at sea.
"That sort of behaviour makes it difficult or makes it worrisome that you could see something eventuate at sea."
China is spending considerable sums of money developing its military resources.
In relation to global defence expenditure, it is behind only the US in the rankings.
The CSG is on its way from Singapore to Japan – where it has been invited to participate in military exercises.
Is an actual conflict over passage through the South China Sea likely?
Ms Nouwens added: "There is a lot of reporting in Chinese press that China should not allow itself to be bullied, that it has to present a strong show of force, so there is that nationalistic element of 'we must not let others push us around'.
"Having said that, though, again in terms of what China actually wants to happen, it does not want to be involved in a conflict, it does not want to be seen as actually leading any sort of contingency at sea."
These are tense times for the fleet, while China watches its movements with a close eye.