In March 18, 2017, North Korean leader Kim Jong Un observed the test of a new type of liquid propellant engine. Mounted on a static test stand, the engine featured one large thrust nozzle flanked by four smaller vernier engines.

It had never been seen before, and North Korea watchers weren’t sure at the time what exactly to make of the test. Yes, the engine appeared like a plausible candidate to power the first stage of an intercontinental-range ballistic missile or even an intermediate-range ballistic missile, but North Korea did not offer any clear indication it was designed