During the Korean War, United Nations (UN) forces fought 3 communist allies: North Korea, China and the Soviet Union. North Korea deployed a heavily armed, Soviet-trained conventional army. China committed 2 million light-infantry troops. The Soviet Union covertly provided air combat, strategic planning and logistics. Fighting took place across a mountainous peninsula shaped by major rivers, poor road networks and extreme weather ranging from hot summers to sub-zero winters. UN forces controlled the seas, while communist troops effectively exploited the rugged mountains.
The three communist nations which went to war with the United Nations were North Korea, China and the Soviet Union ...
North Korea
In June 1950, North Korea launched 223,000 soldiers supported by 150 tanks across the border into South Korea. The North Korean People's Army (KPA) was a conventional army equipped with Russian tanks, artillery and tactical aircraft.
Many North Korean soldiers were hardened veterans of the war against Japan and the Chinese Civil War. KPA soldiers were well trained and equipped.
Tactics were based on Soviet doctrine, which emphasised rapid advances spearheaded by armoured and infantry assaults. The quality and power of the KPA's initial invasion forced its opponents back to the southern tip of the Korean peninsula.
When Inchon and Seoul were recaptured by UN forces, the KPA's supply line was cut, and it could not resist the powerful UN counterattack that followed. A hasty and disorganised retreat caused massive casualties and materiel losses for the KPA.
The KPA reorganised after the Chinese intervention, and for the remainder of the war it played a much-reduced role in operations.
China
During the Korean War, the Chinese People's Volunteer Army (PVA) sent 2 million soldiers to Korea. The PVA was a light infantry army with only a limited number of heavy weapons, such as artillery, very few anti-aircraft guns, and no armoured vehicles. Compared to the UN forces it faced, the Chinese army was primitive in its communications, logistics and medical infrastructure.
A PVA Infantry Division had 10,000 men. The initial 35 divisions committed to Korea were well equipped, but later units had to send men into battle armed only with grenades.
Nevertheless, the Chinese soldier was a tenacious and formidable enemy. They were usually physically tough and committed to the cause. The officers were competent and experienced.
Chinese tactics relied on overwhelming the enemy with numbers. The Chinese frequently launched human-wave assaults against their foes, considering losses secondary to achieving battlefield success.
Soviet Union
Despite its denials at the time, the Union of Soviet Socialist Republics (USSR) was deeply involved in the Korean War, and its contribution was vital.
The USSR provided diplomatic support, strategic and grand tactical planning, including the planning of the invasion of South Korea, and essential logistical support. It supplied and trained the air forces of China and North Korea. Soviet pilots flew aircraft with Chinese or North Korean markings.
After the war, the Soviets claimed to have shot down over 400 UN aircraft.
Theatre of war
The Korean Peninsula is 856 kilometres long, bordered by the Sea of Japan* in the east, the Korea Strait in the south and the Yellow Sea to the west. Mainland Japan lies 160 kilometres across the Korea Strait...
The northern border with China runs along the Yalu River.
In the north-east, an 18-km border with Russia (then the USSR) allowed Soviet supplies to reach North Korea.
Korea has 9,200 kilometres of mostly inhospitable coastline and more than 3,500 offshore islands. The waist of the peninsula, where most of the war was fought, is generally 350 km wide and, at its narrowest, 200 km.
The Taebaek Range, up to 1,708 m above sea level, runs down the east side of the peninsula, and smaller ranges head west from it, creating a barrier to the movement of armies along the country's central spine.
In 1950, road and rail lines were few and tended to run north-south along both coasts with few east-west connections.
On the east coast the close proximity of mountains to the sea broke up the coastal plain. The mountains slope down more gently to the west coast, where wide plains and broad, shallow tidal estuaries exist.
Most major rivers flow from north-east to south-west, forming another series of obstacles to north-south movement, especially within the mountains where road and rail bridges were rare.
Seoul, the South Korean capital, was an important political objective for both sides. It was also of great practical importance as the focal point of all west coast communications. Ports were few. Fortunately for the UN, Korea's greatest port Pusan (Busan) was in the south-east corner of the country, close to Japan, the UN's base for supply. Pusan was never taken by the communists.
Korea has extreme climate variations. In summer, it is rainy, hot and humid. Winter brings bitter winds to Korea from Siberia and Mongolia. The winter temperature in the mountains can be extremely cold - minus 17 Celsius is normal, and snow covers the mountains throughout winter.
Because the North Korean and Chinese armies were lightly equipped and less motorised, they found it easier to operate in the mountains than the UN forces, which depended on road and rail for movement and supply.
In the first year of the war – the war of movement – the UN tended to launch its attacks up the coasts where, as the UN had complete control of the sea lanes, it could also use sea transport and supply. This left a gap in the intervening mountains which the communists exploited in their first counteroffensive from October 1950.
In the second static phase of the war, the communists continued to launch offensives in the mountains where, because of a poor road network often closed by snow in winter, UN forces could not easily reinforce their troops once the axis of the communist attack was revealed.
* The Australian Government and the Department of Veterans' Affairs do not take a position on whether the body of water between Japan and the Republic of Korea should be referred to as the ‘Sea of Japan’ or the ‘East Sea’.