North Korea is powerless to prevent a U.S. strike on its nuclear program, but retaliation is well within its means. The significant military capability that North Korea has built up against South Korea is not advanced by Western standards, but there are practical ways Pyongyang could respond to aggression.
The North Korean military's most powerful tool is artillery. It cannot level Seoul as some reports have claimed, but it could do significant damage.
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Tube and Rocket Artillery
The biggest anticipated cost of a North Korean artillery barrage in response to an attack would be the at least partial destruction of Seoul. But the volume of fire that the North can direct against the South Korean capital is limited by some important factors. Of the vast artillery force deployed by the North along the border, only a small portion — Koksan 170-mm self-propelled guns, as well as 240-mm and 300-mm multiple launch rocket systems — are capable of actually reaching Seoul. Broadly speaking, the bulk of Pyongyang's artillery can reach only into the northern border area of South Korea or the northern outskirts of Seoul.
All forms of North Korean artillery have problems with volume and effectiveness of fire, but those issues are often more pronounced for the longer-range systems. Problems include the high malfunction rate of indigenous ammunition, poorly trained artillery crews, and a reluctance to expend critical artillery assets by exposing their positions.
Based on the few artillery skirmishes that have occurred, roughly 25 percent of North Korean shells and rockets fail to detonate on target. Even allowing for improvements and assuming a massive counterstrike artillery volley would be more successful, a failure rate as high as 15 percent would take a significant bite out of the actual explosive power on target. The rate of fire and accuracy of North Korean artillery systems is also expected to be subpar. This belief is founded on the observably poor performance of North Korean artillery crews during past skirmishes and exercises. Though inaccuracy is less noticeable in a tactical sense — especially as part of a "countervalue attack," where civilian areas are targeted — at the higher level an artillery retaliation rapidly becomes a numbers game.
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Although North Korea could technically open fire on South Korea with all of its artillery systems at once, this would open Pyongyang up to significant counter-battery fire and airstrikes that could rapidly reduce the artillery force it has so painstakingly built up. Instead, as other studies have shown, only a portion of North Korean artillery would be used at a time. This is particularly true for the advanced systems that are most important to Pyongyang: long-range artillery that is able to strike at Seoul. The heavier, more advanced systems are not only difficult to replace, but they are also priority targets for counter-battery fire and airstrikes. Even when firing, artillery systems would be able to do so only temporarily before relocating or otherwise trying to hide the system's firing location to avoid destruction.