Pusan
It was a large-scale battle between United Nations and North Korean forces lasting from August 4 to September 18, 1950. It was one of the first major engagements of the Korean War. UN forces, having been repeatedly defeated by the advancing North Korean People's Army, were forced back to the "Pusan Perimeter", a 140-mile (230 km) defensive line around an area on the southeastern tip of the Korean Peninsula that included the port of Pusan. The UN troops, consisting mostly of forces of the Republic of Korea Army (ROK), United States Army (US), and British Army, mounted a last stand around the perimeter, fighting off repeated North Korean attacks for six weeks as they were engaged around the cities of Taegu,Masan, and P'ohang, and the Naktong River. The massive North Korean assaults were unsuccessful in forcing the United Nations troops back further from the perimeter, despite two major pushes in August and September. North Korean troops, hampered by supply shortages and massive losses, continually staged attacks on UN forces in an attempt to penetrate the perimeter and collapse the line. However, the UN used the port to amass an overwhelming advantage in troops, equipment, and logistics, and its navy and air forces remained unchallenged by the North Koreans during the fight. After six weeks, the North Korean force collapsed and retreated in defeat after the UN force launched a counterattack at Inchon on September 15. The battle would be the furthest the North Korean troops would advance in the war, as subsequent fighting ground the war into a stalemate.
Inchon
The battle was an amphibious invasion and battle of the Korean War that resulted in a decisive victory and strategic reversal in favor of the United Nations (UN). The operation involved some 75,000 troops and 261 naval vessels, and led to the recapture of the South Korean capital Seoul two weeks later. The battle began on September 15, 1950, and ended September 19. Through a surprise amphibious assault far from the Pusan Perimeter that UN and South Korean forces were desperately defending, the largely undefended city of Incheon was secured after being bombed by UN forces. The battle ended a string of victories by the invading North Korean People's Army. The subsequent UN recapture of Seoul partially severed NKPA's supply lines in South Korea. The majority of United Nations ground forces involved were U.S. Marines, commanded by General of the Army Douglas MacArthur. MacArthur was the driving force behind the operation, overcoming the strong misgivings of more cautious generals to a risky assault over extremely unfavorable terrain.
Operation killer
The primary objective of Operation Killer was to annihilate enemy forces below the Arizona line. However, the enemy had begun a general withdrawal, offering only scant resistance in the area and immediately on the end of this Operation Ridgway initiated Operation Ripper, which was basically to advance and secure positions suitable for staging a general assault to recapture Seoul and again reach the 38th Parallel.
Chosin
Chosin was a decisive battle in the Korean War. Shortly after the People's Republic of China entered the conflict, the People's Volunteer Army 9th Army infiltrated the northeastern part of North Korea and surprised the US X Corps at the Chosin Reservoir area. A brutal 17 day battle in freezing weather soon followed. In the period between 27 November and 13 December 1950, 30,000. United Nations (UN) troops (nicknamed "The Chosin Few") under the command of Major General Edward Almond were encircled by approximately 67,000, Chinese troops under the command of Song Shi-Lun. Although Chinese troops managed to surround and outnumber the UN forces, the UN forces broke out of the encirclement while inflicting crippling losses on the Chinese. The evacuation of the X Corps from the port of Hungnam marked the complete withdrawal of UN troops from North Korea.
Operation Roundup
The attack was in the center of the country, where the X Corps and the ROK III Corps launched Operation Roundup. It found the going would be difficult against the Chinese troops. In fact, the Chinese launched what was known as their fourth offensive, the Battle of Chipyoongi. The UN managed to stop this attack and once again regain the advantage.