Key point: South Korea's conventional capabilities outmatch those of the North.
In the last seventy years, the Republic of Korea Army (ROK Army) has evolved from a constabulary force into one of the largest, most powerful, technologically advanced armies in the world. This remarkable evolution is entirely due to the original 1950–53 invasion and war by neighboring North Korea. This existential threat has never truly gone away, with North Korea consistently threatening—and preparing for—a second, successful invasion.
The Republic of Korea Army was established in 1945 by U.S. forces occupying the southern half of the Korean Peninsula. By 1946 the ROK Army had nine “national security regiments,” lightly armed infantry regiments with a total manpower of 25,000 troops. As U.S./Soviet relations worsened, this was increased to 50,000 troops.
The invasion of North Korea in June 1950 caught the fledgling ROK Army ill-prepared for a conventional invasion. In particular, the army lacked the anti-tank firepower necessary to deal with the Korean People’s Army’s 105th Armored Brigade, which fielded approximately 120 Soviet-made T-34/85 tanks and SU-76 self-propelled guns. Although a small armored force by World War II standards, the ROK had virtually nothing to counter it with and was rapidly pushed south towards the port town of Busan.
The next three years saw intensive efforts by the United States to train and expand the ROK Army to modern standards, not the least of which so that the army could assume the bulk of the responsibility for the country’s defense. These efforts were successful, and within a few years of the Korean War’s end the U.S. Army on the peninsula had been scaled down to two, and later just one division.