Last year, former Defense Secretary Robert Gates was greeted in Beijing by China's experimental stealth jet buzzing over his head. Gates didn't sweat it: He proclaimed that the J-20 wouldn't be ready until at least 2020. Oops.

The Pentagon's top China official has now revised that estimate. The J-20, China's first stealth jet, will be operationally ready "no sooner than 2018," David Helvey, deputy secretary of defense for East Asia and Asia Pacific Security Affairs, told reporters Friday.

The new anticipated timetable for the J-20 hardly augurs the end of American military dominance. But it wasn't the only Chinese military development that took the Pentagon by surprise last year.

According to the Pentagon's new report (.pdf) on the Chinese military, China's got three nuclear-powered submarines – an advance that Helvey conceded the U.S. military didn't anticipate. China also fielded an "improved" amphibious assault vessel last year, while the U.S. Marine Corps is having trouble upgrading its own.

And that's just the stuff that the Pentagon can see. Helvey speculated that the Chinese military keeps its research, foreign military acquisitions and nuclear modernization off its books. The report estimates that China's declared $106 billion annual military budget is really more like $120 to $180 billion.

None of that means China's military will overtake America's anytime soon. China won't, for instance, have a global communications and navigation satellite network until 2020, which means it doesn't have a prayer of having a truly global Navy until at least then – even if it starts building its own aircraft carriers. Helvey disclosed that China still has neither built nor acquired any armed drones, and the spy robo-planes it has are the Harpies that Israel sold it nearly a decade ago. And while China may have an amphibious ship, the report says it can't actually invade or hold nearby Taiwan, let alone any target further away or better defended.

At the same time, it's hard not to notice that America's own stealth fleet keeps racking up #fails.

First there's the Air Force's F-22 Raptor. It's choking its pilots, and the Air Force doesn't know why. Gates' successor, Leon Panetta, this week restricted Raptor flights and hurried up an installation of a backup oxygen system onto the jets – which won't be complete until at least 2014. Panetta did not ground the F-22, so the nearly 200 planes will definitely be in Air Force's arsenal ahead of the J-20. But until the mysterious oxygen problems are decisively fixed, pilots may be wary of flying them, and the Air Force leadership may be wary of ordering it into combat.

Then there's the F-35 Joint Strike Fighter, a family of jets for the Air Force, Navy and Marines. It's already the most expensive weapons program in human history – current estimates peg the F-35's lifetime costs over decades at $1.1 trillion-with-a-T – and not a single one of the advanced, powerful stealth jets is in the air. The Marines' variant was so riddled with cost-overruns that it was put on a timeout in 2011; it's off probation now. But testers keep finding expensive engineering flaws with the family of jets, and the Pentagon has given up predicting when it will actually patrol the skies.

The U.S. doesn't want conflict with the Chinese, whose economy is inextricably tied to its own. But it might not see one coming. Especially not if China's stealth planes are advancing while its own are stalling.