The KATUSA program arose from a shared history of war with North Korea. Both American and South Korean troops fought together, so it made sense to make it official.

Gen. Douglas MacArthur and South Korean Pres. Syngman Rhee crafted the arrangement in 1950, and both viewed these “augmentees” as critical to their shared war efforts.

In June 1950, a North Korean blitzkrieg had pushed Washington and Seoul’s ill-prepared troops into a tiny pocket around the port city of Busan at the southeastern tip of the peninsula.

With Pyongyang’s forces closing in, MacArthur was desperate for more manpower. Rhee wanted to find ways to improve his fledgling army.

The chaos of war, along with a cultural and language barriers—and just flat out racism—caused serious difficulties for the program. While in need of extra soldiers, many American commanders distrusted or dismissed the Korean volunteers.

“An inordinately large percentage of men, particularly in some units, stated at KATUSAs were no good, that they would sleep on guard, ‘bug out,’ refuse to work or pretend not to know what was expected of them,” an Army team sent to evaluate the service’s performance reported.

Despite orders from Pres. Harry Truman to integrate, Eighth Army had arrived in Korea with official racial boundaries still firmly in place.

“This mistrust may stem from fact or it may result from pre-existing attitudes,” the team explained. “Many people made the statement that a KATUSA or Puerto Rican or Negro is either an excellent fighter, or he is no good at all.”

“If such ‘extremes’ exist it seems highly likely that they are not inherited.”

In spite of these barriers, more than 6,000 KATUSAs had given their lives by the end of the war. After the Korean Armistice Agreement stopped the shooting, the Pentagon kept the program going as an established method of training South Korean troops.

Nearly 10 years after the armistice, Washington and Seoul agreed to use the arrangement to bulk up Army units throughout the country. In 1968, there were still more than 10,000 KATUSAs aiding the ground combat branch in Korea, according to one Pentagon memo.

The relative skill level between South Korean troops and their American comrades—and perhaps continuing mistrust—was still an issue. “KATUSA personnel cannot be used in intelligence units to replace U.S. personnel,” the Pentagon memo declared.

And for decades, the U.S. essentially had veto power over the South Korean military. The American officer in charge of the Eighth Army — who had a shared headquarters with South Korean troops called the Combined Forces Command — was the de facto highest ranking military official in the country.

In 1994, the two countries finally agreed to allow South Korea—an established sovereign state and growing regional economic powerhouse—to oversee its own military affairs … during peacetime.

Today, if another war broke out on the peninsula, the Pentagon would still direct South Korean troops at the highest levels.