A solid fuel, road mobile ICBM with a 150kt thermonuclear warhead is no small achievement.
It took the US and Russia 30 years to get to that point (start point 1950).
Yes, we know the Norklandians did not get there in 20 years without help. It’s inconceivable.
It COULD be done by shipping only people/brains, machine tools, designs and process knowledge to Norklandia.
That way nobody sees major components in shipment.