North Korea's latest nuclear test was estimated to equal 6 or 7 kilotons of TNT, which makes it neither a failure nor a resounding success, according to experts.
"There is no such thing as a failed nuclear test," said Kim Tae-woo, former head of the Korea Institute for National Unification. "Even if there was no nuclear blast, scientists can gather data on what went wrong, and this is how the North has been able to continue developing nuclear weapons."
The force generated by the latest nuclear test was less than half the 15,000 tons of the bomb that was dropped on Hiroshima in 1945. But if such a weapon was dropped on Seoul, it would still be enough to level several square kilometers and lead to hundreds of thousands of casualties.
South Korean and U.S. intelligence believed until now that North Korea's nuclear weapons were rudimentary at best, weighing only two to three tons each. That would make it impossible to mount them atop an intercontinental ballistic missile or attach to a fighter jet. Instead, they would have to be transported via a bomber such as the Ilyushin IL-28. The allies know where North Korea's IL-28 bombers are based and are confident that they can take them out.
But the whole picture changes if North Korea acquires the technology to miniaturize a nuclear warhead and mount it on top of a ballistic missile, because the South Korean military currently lacks the ability to thwart such an attack.