China has enough planes and shipping to get over 10 million troops to our west coast all at once.
I guess, theoretically, it can be done. Provided that:
- the US Government will sit on their hands while watching the Chinese go about the years of planning, months of preparation and training, weeks of assembling and loading the ships and planes that any such invasion would require.
- the US CVNs will pretend they are fishing trawlers and turn the blind eye as the whole invasion fleet will sail across the Pacific
- the US SSNs will urgently find something important to do in the Atlantic or elsewhere and their ELFs will mysteriously break down, so they won't be able to intercept the coming armada.
- the US SAC will decide to ground its fleet for maintenance and to consider the satellite images of the approaching Chinese fleet a hallucination.
Remember that the largest ever successful amphibian invasion in the world's history to date was the Normandy D-Day and that involved 160,000 troops + 25,000 paras + 200,000 navy crew and 5,000 ships. The distance between the staging and landing area was only a few hundred km. The invasion took place in the middle of a war with the target (Germany) already being engaged on 3 major fronts.
To transport 10 million troops the Chinese will need a 1000 ships, each the size of Queen Mary - I am not aware they have nearly as many available. For smaller ships we are talking about maybe 50,000?
But even more interesting question is why would the Chinese want to do it all and what will they achieve with the invasion?
Imagine that, somehow, they've managed to disembark, unopposed, their 10 million poorly trained teenage conscripts on the shores of California. They will now face the need to fight their way across the continent to seize the seat of the Government on the opposite coast while maintaining a constant supply train across the Pacific. This is not likely to be a great success.
But imagine then that they've done it. The US is now under the Chinese occupational authority - now what? Do they use it for lebensraum (Siberia or Australia would make easier targets)? Do they take the oil (better take Indonesia and Malaysia for that or, simpler, - just buy the stuff in the Middle East)? Do they enslave the population to assemble iPads in horrible conditions (they have plenty of workforce for that)?
At the same time they will devalue a large portion of the foreign currency reserves they are sitting on, will kill the cash cow which feeds their export-oriented economy, will not make any friends in the world (well, may be some but who needs friends like that?). And, last but not least, with all these troops away from the homeland - who is going to keep the local population in check? It just does not add up.
I think, no matter how tough it is, but the Americans are just going to have to learn to live with the thought that no one in the world wants to invade their country (other than the illegal immigrants, that is).
Regards