When President Obama met with South Korean President Park Geun-hye on Tuesday, one item was high on the agenda: how to handle North Korea, which has in recent months threatened to strike both countries.
Obama called such threats "a dead end."
"We remain open to North Korea taking a peaceful path of denuclearization," the president told reporters.
But could the North's missiles reach U.S. territory? That question has proved hard to answer.
North Korea has demonstrated its ability to build short- and medium-range missiles, and it has launched a small satellite into space. But neither of these achievements would necessarily allow it to reach the U.S. with a warhead.
At a parade in April 2012, North Korea unveiled a new kind of missile. The so-called KN-08 sat on an enormous military truck, which would allow it to be moved around the country. And it looked like it had been designed to deliver a warhead to a distant target, even as far as the U.S. Everyone knew North Korea was working toward this kind of missile, but nobody knew whether it could actually build one.
"At first I thought, 'Wow, they finally managed it,' " says Markus Schiller, an aerospace engineer working for Schmucker Technologie, a German company that consults on security issues. As soon as he heard about the parade, Schiller started looking for images of the missiles.
"It's unbelievable how much [information] you can actually get out of the Internet," he says.
Looking at videos and still photos online, Schiller started to notice that some things seemed off. Six of the new KN-08 missiles were in the parade, but each looked a little different from the next.
"The first stage of missile one was longer than the first stage of missile two, and so on," he says.
Schiller wasn't the only one to see discrepancies. David Wright, a rocket expert at the Union of Concerned Scientists, has spent a lot of time studying North Korea's missile technology. "There were a lot of little details that if you looked carefully not only didn't make sense on each missile but didn't agree between the missiles," he says.
Fuel ports were in weird places, for example. Cables looked like they weren't laid correctly. And the missile's warheads appeared to be made of cheap metal sheeting, or perhaps wood. In fact, there were so many problems that most experts agree: The missiles on parade weren't real.
"The complicating factor is that it is a normal thing to make simulators before you make real missiles," says Jeffrey Lewis, director of the East Asian nonproliferation program at the James Martin Center for Nonproliferation Studies at the Monterey Institute of International Studies.
Engineers everywhere routinely use dummy missiles to figure out how to fit the real ones together. Crews can train with them. So the question is, were the missiles on parade pure fiction, or mock-ups built as part of a real weapons program? The U.S. intelligence community believes the latter.
Speaking at a press briefing in March, Admiral James Winnefeld, vice chairman of the Joint Chiefs of Staff, said the intelligence community does believe this missile program is real, even if the missiles in the parade turn out to be fake. But he wouldn't say how far along he thinks North Korea's program has developed.
"Our assessment of where it exists in its lifetime is something that would remain classified," he said.
Those without access to military data remain divided. Jeffrey Lewis says he believes the missiles are part of a real program, but Schiller, the aerospace engineer who first spotted the problems, is doubtful. If these really were mock-ups, he says, all the missiles would look identical. The fact that they don't makes him think it's a ruse.
These kinds of uncertainties, Wright says, will make it that much more difficult to decide how to respond to North Korea the next time tensions flare.