On December 7, North Korea claimed to have conducted a “very important test” at its Sohae Satellite Launching Station that “will have an important impact on changing the strategic position of the DPRK.”[1] The North Koreans did not describe what was tested, but prior open-source imagery suggests it was a static (ground) test of a large liquid-propellant rocket engine.[2] It remains to be seen what rocket system the engine was associated with: a previously launched intercontinental ballistic missile (ICBM), intermediate-range ballistic missile, space launch vehicle, or a new system. In any case, the static test could be the precursor to...