O noes! China has finally got to where the US was in 1985, and the UK was in about 2000! Surely time for a big military panic?
A force of J-20s would find this hedge impenetrable: as soon as they penetrated to any depth, the "stealth" planes would be showing a non-stealthy aspect to radars on their flank or behind them, or would find their hot exhausts picked up by US/allied IRST. The lumbering Chinese jets would then be pounced upon and eliminated. If somehow the J-20 is as capable as a Raptor and the People's Republic should manage to inflict any damage on US forces or their allies, the responding shower of seaborne cruise missiles would wipe China's air capability off the map – leaving Beijing a stark choice between humiliation and suicidal escalation to nuclear ballistic-missile strikes on the US mainland.
The reality is that western global hegemony over the seas and the skies above them would be pretty much unchallenged even if the J-20 actually was a rival to western stealth technology. America alone, even following the just-announced reining in of defence spending, intends in the near future to field a force of more than 2,000 genuine modern stealth warplanes backed by many hundreds more modern combat aircraft of other types. A thousand more stealth fighters (F-35s) are set to be ordered by US allies worldwide, and these allies also dispose of yet thousands more highly capable, modern non-stealth planes.
The USA and her allies in the 2020s will have more than 3,000 genuine operational stealth fighters and many thousands more highly capable, sophisticated non-stealth aircraft plus warships, cruise missiles etc in profusion. China and Russia, by that point, will probably not have any substantial numbers of real operational stealth aircraft at all – both nations have only just got early prototypes flying, putting them where the USA was in the 1980s and Europe was a decade ago. Both nations together possess no more than 3,000 functioning combat aircraft, mostly obsolete, all poorly maintained, and in Russia's case at least, flown by pilots who log no more than a few hours a year. The Russian and Chinese navies are in even worse shape.
Even if Russia and China could cooperate effectively (they can't or won't) and had some reason to take on the West (so cutting their own economies off at the knees) – even if Russian and Chinese technology and military readiness was equivalent or superior to Western (it plainly isn't anywhere near) – the west would still win a conventional air/sea war by simple weight of numbers. In the case of Russia or China acting alone, the fight would be even more one-sided.
The usual suspects are, of course, furiously bigging-up the J-20 as a possible menace. The erratic Carlo Kopp of Australia, famous for predicting that terrorists would be fabricating electromagnetic pulse bombs in garage workshops by now, considers that the J-20 amply justifies a much larger fleet of F-22 Raptors. (No surprise there: no matter what happens, Kopp generally considers that the answer is more F-22s.) Retired US air force generals are pushing this line too, of course. The hugely bloated western military aerospace industry, its revenues sapped by economic conditions and a belated focus on the ground troops who are actually fighting real wars in southwest Asia, will naturally seize upon even the flimsiest excuse to plead for yet more billions to be spent moving the western state of the air-combat art still further onward – no matter that it is decades ahead of any possible opposition.
But to those of us not employed directly or indirectly by air forces and aerospace companies, the idea that we western taxpayers should really be spending any more than is now planned on air forces is a hard one to swallow – the more so if it means more cuts to other parts of government, especially our hard-pressed ground troops in Afghanistan. Unlike the flyboys, the army are not trying to set up a condition where they can win a vanishingly unlikely war without taking any losses: they are trying to win a war which is actually happening, and suffering losses every day.
When our soldiers and marines (or, occasionally, airmen or sailors) on the ground in Afghanistan can win easily without significant losses – rather than being badly bloodied for sometimes unimpressive results as we see now – then it might be time to think about experimental Chinese stealth prototypes. When Russian and Chinese military spending combined approaches even half the amount spent by the USA on its own*, it might be time to wonder whether the Asian powers might in some way, one day, militarily menace the west.
Until then, we've all got more important things to worry about than the J-20. ®
*As of today, Russia and China together are estimated (pdf) to spend less than a quarter of what the US spends on defence. Even lackadaisical, can't-really-be-bothered-seeing-to-our-own-defences Europeans are big players compared to China; France and the UK together comfortably outspend the People's Republic.