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In 2018, at a summit in Quebec, he exited the gathering to meet North Korea's leader Kim Jong Un.

The intrigue has less to do with the failure itself and more with how Kim Jong Un reacted.

"Kim Jong Un believes nuclear weapons are the only way he can protect his country, and yet all it has at sea is an old submarine and some small support ships," said Choi Il, a retired South Korean navy captain.

This would therefore have been "a very embarrassing incident" for Kim Jong Un, he said, as it "highlights the limitations of North Korea's shipbuilding".

But experts in North Korea propaganda believe there is far more to Kim Jong Un's outburst than raw anger and humiliation.