How South Korea Thwarted Kim Il-sung’s Shadow War
North Korea’s late-1960s commando campaign came to a bloody halt
In the late spring of 1969, a 75-ton North Korean speed boat hurtled through the Yellow Sea off the western coast of South Korea on a secret mission. Its 15-man crew on board was supposed to pick up an agent operating in the South on behalf of Pyongyang’s spy services and take him back north. 
It was an operation similar to many others that North Korean intelligence had carried out over the past two years as it flooded its enemy, the Republic of Korea, with infiltrators.
The boat’s crew came ashore on at midnight Heuksan Island looking for its agent. Instead, they found South Korean security forces and a firefight waiting for them. 
All 15 were killed in the shootout. 
The operation’s failure was no accident. South Korean intelligence had laid what the CIA later called “a carefully prepared trap” for the exfiltration team. A month prior, the Korean Central Intelligence Agency, or KCIA, had captured the agent the team was supposed to pick up, turned him into a double agent and used him as bait. 
Since the fall of 1966, North Korea had waged a guerrilla campaign against South Korea in an attempt to needle the South Korean and American militaries and foment popular unrest against the government of Pres. Park Chung-hee. But South Korea was getting better at finding and disrupting Pyongyang’s agents. And North Korea’s floundering war effort was coming to a close.
The remaining years of the 1960s would see more bouts of violence from North Korean forces. The 124th Army Unit which had tried to kill Park would try one last, desperate guerrilla raid inside the ROK. And North Korean forces would once again attack Americans, shooting down a Navy EC-121 spy plane.
But by the beginning of the 1970s, it was clear that Kim Il-sung’s guerrilla campaign had come to a close, having ended in failure.
The assassins North Korea sent to kill the South Korean president came perilously close to the presidential residence, but their mission was a flop. Park was still alive after the raid and the South Korean people rallied around him afterwards in revulsion at the attempt, rather than rising up against his government. 
In a 1970 National Intelligence Estimate, the CIA assessed that North Korea had mostly given up on the campaign of dramatic raids and terrorist attacks as means of undermining the ROK. Violence at the border had plummeted and North Korea was sending infiltrators for political espionage in the ROK rather than guerrilla warfare. 
Read the Remainder at War is Boring