A missile is launched during a drill in this undated photo released by North Korea's Korean Central News Agency in Pyongyang on August 30, 2017. Photo: KCNA via Reuters

The North Korean missile that overflew Japan on August 28 may have tested a “post-boost vehicle” or PBV that improves accuracy and theoretically allows future missiles to carry decoy warheads that thwart missile defenses, according to an article published by 38 North.

The detailed assessment by missile defense expert Michael Elleman on the Johns Hopkins University website dedicated to North Korea notes that the missile broke up into three pieces during flight and flew only 2,700 kilometers — far short of its 4,000 kilometer range.

Elleman examined various explanations of why this happened — from an early shutdown of the missile’s engines by North Korean engineers to the use of a heavier payload. But he noted that the truncated flight path might also be the result of a malfunctioning PBV.

“An alternative disturbing hypothesis is that tests of the missile have included a small post-boost vehicle (PBV) to provide extra boost to the payload after the main stage is discarded,” Elleman wrote.

“There are logical reasons for employing a PBV,” Elleman added. “In addition to boosting range, it can be used to make fine adjustments to the payload’s velocity after engine shut-down. ICBMs fielded by the US, Russia, France and China all employ PBVs to achieve better accuracy. PBVs also provide a platform to carry a warhead, plus lightweight decoys or other penetration aids capable of impairing effectiveness against missile defenses.”

“The presence of a PBV on the Hwasong-12 is just a hypothesis for now, although reports that the missile “broke into three pieces” are consistent with PBV engine failure,” Elleman said.