Trieste...
"*Impressive, but some way short of the all-time record, achieved in 1960 by the US's bathyscaphe Trieste which, with its crew of two, hit the bottom of the Marianas Trench at 10,900m (35,800ft)."
Yes, but Trieste wasn't REALLY American - it was built by a French father and son, who built it in...the city of Trieste, France. They could not keep paying for it's improvements and upkeep however, and sold an interest in it to the US Navy. Flush with the cash of the Americans, the Frenchmen made some further improvements, and with the son piloting, he and an American Navy officer decended once, and only once, to the bottom of the Marianas Trench. They disturbed some flatworms as they touched down, proving that life could exist at amazing depths, but conducted no other science. Hence, no one has returned, because we just didn't learn a hell of a lot.
If the Chinese need undersea tech, they certainly don't have to buy it from the US, they can always head to France and other EU states...