What was the first major battle between US and North Korean forces?

The Battle of Osan was the first major battle between US and North Korean forces in the Korean War.

It took place on 5 July 1950, shortly after North Korea invaded South Korea. The American force was Task Force Smith, centered on the 1st Battalion, 21st Infantry Regiment, with artillery support. The unit had been rushed from Japan to slow the North Korean advance and buy time for additional American troops to reach Korea.

Task Force Smith faced a much larger North Korean force supported by Soviet-built T-34 tanks. American troops had limited anti-tank weapons and were not prepared for the scale or intensity of the fighting. After several hours, North Korean forces outflanked the position and forced the surviving Americans to withdraw. The battle was a North Korean victory, but the delaying action helped reinforce the defense farther south.

The Battle of Osan is sometimes confused with Inchon or the Battle of the Pusan Perimeter. Inchon was the later 1950 landing that changed the war’s momentum, while Pusan was a larger defensive campaign. Osan marked the first US ground engagement with North Korean forces.