South Korea's secret weapon for defeating North Korea

National Interests:

In modern Korea’s relatively short history, amphibious warfare has played a key and pivotal role. The United Nations essentially liberated South Korea from invasion with a single amphibious stroke, and the country has maintained a large and powerful Marine Corps ever since. Now, a new generation of South Korean amphibious naval forces means the country can ponder taking the offensive during wartime, not only blunting an invasion but upending the Kim family’s dynastic hold on North Korea.

Korea’s peninsular nature means that the ocean is never far away from residents of both countries. It also means that armies fighting on the peninsula, friendly or not, run lines of communication and supply that are constantly in danger of being severed from the sea. Gen. Douglas MacArthur, well aware that the invading Korean People’s Army was reliant on increasingly tenuous supply lines as it inched south, planned and oversaw a successful amphibious assault at the port of Inchon. The result was an abrupt reversal of fortune for a KPA on the brink of victory, with the shattered remnants of Kim Il-sung’s army racing north to avoid entrapment and annihilation.

Korea, just 160 miles wide and mountainous, doesn’t leave much room for maneuver—that is, unless you count the coastline: the North and South have more than three thousand miles of coastline combined. In any future Korean war, amphibious operations will help avoid costly wars of attrition, avoiding force-on-force fights to instead focus force on an enemy’s center of gravity—like Seoul or Pyongyang.

Under the mentorship of the U.S. Marine Corps, South Korea has maintained one of the largest marine forces in the world. As one USMC colonel put it during the Vietnam War, which saw a brigade’s worth of South Korean marines (and their U.S.-trained officers) sent to Southeast Asia, “We taught them everything we know, and now they know it better than us.” Today, the Republic of Korea Marine Corps (ROKMC) consists of twenty-nine thousand marines organized into two divisions and a brigade.
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This new strategy requires even more of the ROKMC. The new plan is to ROK marine and naval forces to directly invade Pyongyang from the sea, killing or capturing the regime’s leadership before it can use nukes. Towards this end, the Marine Corps has established a new brigade-sized unit code-named “Spartan 3000,” whose mission is the destruction of “key military facilities in the North’s rear during contingencies.” This almost certainly sounds like operations in and around Pyongyang. The brigade will be able to deploy on just a day’s notice from its base at Pohang, far from the demilitarized zone.
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There is more.

The ROK Marines have a good reputation with US Marines.  The threat of amphibious forces alone will cause the Norks to have to keep reserve forces at locations along their coastline that they would otherwise commit to an invasion force.