SEOUL, South Korea (AP) — With North Korea threatening to send a salvo of ballistic missiles close to Guam, a U.S. military hub in the Pacific, pressure could grow for Washington to put its multibillion-dollar missile defense system into use and shoot them out of the air.

If U.S. territory is threatened, countermeasures are a no-brainer. But if the missiles aren't expected to hit the island — the stated goal is to have them hit waters well offshore — should it? Could it?

It's not an easy call.

North Korea claims it is in the final stages of preparing a plan to launch four intermediate-range ba...