The Battle of Chongju (Korean: 정주 전투, 29–30 October 1950), also spelled Battle of Jeongju took place during the United Nations Command (UN) offensive towards the Yalu River, which followed the North Korean invasion of South Korea at the start of the Korean War. The battle was fought between Australian forces from 3rd Battalion, Royal Australian Regiment (3 RAR) and the 17th Tank Brigade of the Korean People's Army (KPA) for control of Chongju, North Korea and the surrounding area. After detecting a strong KPA armoured force equipped with T-34 tanks and SU-76 self-propelled guns on a thickly wooded ridgeline astride the line of advance, the Australians launched a series of company attacks with American M4 Sherman tanks and aircraft in support. Despite heavy resistance the KPA were forced to withdraw and the Australians captured their objectives after three hours of fighting.

That evening the KPA were strongly reinforced, attacking the Australian southern flank manned by D Company 3 RAR, and partially penetrating their perimeter. After two hours of fighting the assault was repulsed, and the KPA subsequently launched a furious assault against A Company 3 RAR on the northern position, which also failed amid heavy losses. The following day the Australians advanced to the high ground overlooking Chongju, killing and capturing a number of KPA in skirmishes. That afternoon the town itself was cleared by the remaining elements of the 27th British Commonwealth Brigade without opposition. KPA casualties during the fighting were heavy, while Australian losses included their commanding officer, Lieutenant Colonel Charles Green, who was wounded in the stomach by artillery fire after the battle and died two days later.

The Korean War began early in the morning of 25 June 1950, following the surprise invasion of the Republic of Korea by its northern neighbour, the communist Democratic People's Republic of Korea (DPRK). Numerically superior and better-equipped, the KPA crossed the 38th Parallel and rapidly advanced south, easily overcoming the inferior Republic of Korea Army (ROK). In response, the United Nations (UN) decided to intervene on behalf of South Korea, inviting member states to send forces to restore the situation. As a consequence, American ground forces were hastily deployed in an attempt to prevent the South Koreans from collapsing, however they too were under strength and poorly equipped, and by early August had been forced back by the KPA to an enclave around Pusan, known as the Pusan Perimeter. Key US allies—Britain, Canada and Australia—also committed forces, although these were initially limited to naval contingents and were largely viewed as token efforts in the US. Under diplomatic pressure the British agreed to deploy an infantry brigade in July, and would later dispatch a second brigade as the crisis worsened. The Canadians also agreed to provide an infantry brigade, although the first battalion would not arrive until December 1950. A total of 21 UN member states eventually contributed forces.

Australia was one of the first nations to commit units to the fighting, playing a small but sometimes significant part in the UN forces, which was initially led by General Douglas MacArthur. Forces deployed in Japan as part of the British Commonwealth Occupation Force formed the basis of the Australian response, with P-51 Mustang fighter-bombers from No. 77 Squadron RAAF flying their first missions on 2 July, while the frigate HMAS Shoalhaven and the destroyer HMAS Bataan were also committed to naval operations. During this time the 3rd Battalion, Royal Australian Regiment (3 RAR), which had been preparing to return to Australia prior to the outbreak of the war, remained in Japan, however on 26 July the Australian government announced that it would also commit the understrength and poorly equipped infantry battalion to the fighting, following a period of preparation. Training and re-equipment began immediately, while hundreds of reinforcements were hastily recruited in Australia as part of K Force; they soon began arriving to fill out the battalion. The battalion's commanding officer, Lieutenant Colonel Floyd Walsh, was subsequently replaced by Lieutenant Colonel Charles Green. An officer with extensive operational experience fighting the Japanese in New Guinea during the Second World War, Green took over from Walsh due to the latter's perceived inexperience.

On 23 September 1950, 3 RAR embarked for Korea, concentrating at Pusan on 28 September. There it joined the British 27th Infantry Brigade, a garrison formation hurriedly committed from Hong Kong by the British as the situation deteriorated around the Pusan Perimeter in late August to bolster the US Eighth Army under Lieutenant General Walton Walker. Commanded by Brigadier Basil Coad, the brigade was renamed the 27th British Commonwealth Brigade and consisted of the 1st Battalion, Argyll and Sutherland Highland Regiment (1 ASHR), the 1st Battalion, Middlesex Regiment (1 MR) and 3 RAR. Under strength, the two British battalions had each mustered just 600 men of all ranks, while the brigade was also short on transport and heavy equipment, and had no integral artillery support, for which it would rely entirely on the Americans until the 16th Field Regiment, Royal New Zealand Artillery arrived in January 1951. As such, with a strength of nearly 1,000 men, the addition of 3 RAR gave the brigade increased tactical weight as well as expediently allowing the Australians to work within a familiar organisational environment, rather than being attached to a US formation. Also under the command of the brigade were a number of US Army units, including 155 mm howitzers from the 90th Field Artillery Battalion, M4 Sherman tanks from 89th Tank Battalion and a company from the 72nd Combat Engineer Battalion.

By the time 3 RAR arrived in the theatre, the KPA had been broken and were in rapid retreat, with MacArthur's forces conducting a successful amphibious assault at Inchon and breakout from the Pusan Perimeter on the southern tip of the Korean peninsula. A steady advance began, driving the North Koreans northwards towards the 38th Parallel. The 27th British Commonwealth Brigade was airlifted from Taegu to Kimpo Airfield north of Seoul on 5 October, however its vehicles had to move by road, driving 420 kilometres (260 mi), and did not arrive until 9 October. It was subsequently attached to the US 1st Cavalry Division, under the command of Major General Hobart R. Gay. On 16 October the brigade took over from the US 7th Cavalry Regiment as the vanguard of the UN advance into North Korea, its axis intended to take it through Kaesong, Kumchon County and Hungsu-ri to Sariwon, then through Hwangju to the North Korean capital of Pyongyang. Although the KPA had suffered heavily in the preceding weeks, they continued to resist strongly, while a lack of accurate maps and the narrowness of the roads made rapid movement difficult for the advancing UN forces. During this time 3 RAR had a platoon of American M4 Sherman tanks attached and a battery of field guns in direct support.

The 27th British Commonwealth Brigade subsequently moved 70 kilometres (43 mi) from Kumchon, with the Argylls capturing Sariwon on 17 October, killing 215 KPA and taking many prisoners for the loss of one man killed and three wounded. The brigade then passed to the command of the US 24th Infantry Division on 21 October, under the overall command of Major General John H. Church, while the US 1st Cavalry Division remained in Pyongyang to complete its capture. The 27th British Commonwealth Brigade was subsequently ordered to seize Chongju. Consequently, the brigade continued to advance north with little respite, and on 22 October the Australians fought their first major action at Yongju, killing 150 KPA and capturing 239 of the brigade's 800 prisoners, for the loss of seven men wounded. Intending to defeat the KPA and bring the war to a close, the UN forces pushed towards the Yalu River, on the Chinese border. Resistance continued to be met as the brigade crossed the Chongchon River however, and they now moved towards Pakchon. On 24 October, MacArthur had removed all restrictions on the movement of his forces south of the Yalu River and prepared for the final phase of the UN advance, defying a directive of the US Joint Chiefs of Staff and risking Chinese intervention in support of North Korea.

On the afternoon of 25 October a platoon from 3 RAR was fired on by two companies of KPA as they crossed the Taeryong River to conduct a reconnaissance of the west bank, and although they were subsequently forced to withdraw, the Australians took 10 prisoners with them. Acting as the forward elements of the brigade, that evening Green sent two companies across the river to establish defensive positions, and they subsequently broke up a frontal assault on their positions with mortars while the KPA were in the process of forming up. Sixty KPA supported by a T-34 tank then attacked the forward Australian companies at Kujin early the following morning, resulting in Australian losses of eight killed and 22 wounded. However, the KPA suffered heavy casualties including over 100 killed and 350 captured, and the Australians subsequently succeeded in defending the bridgehead after the KPA withdrew. Intelligence indicated that the British and Australians were facing the KPA 17th Tank Brigade, equipped with 20 tanks, which was preparing a last line of defence at Chongju, 70 kilometres (43 mi) away. Although the KPA had suffered heavy casualties during the previous fighting on the Taeryong River, Coad was now forced to adopt more cautious tactics, advancing in shorter bounds and clearing high points en route. On 27 October the Middlesex continued the advance and was involved in a sharp fight in the hills west of the river near the village of Yongsong-ni. With the war considered all but over the 27th British Commonwealth Brigade continued to pursue the KPA towards Chongju over the next three days, however the advance increasingly encountered strong resistance from KPA infantry dug-in with tanks and self-propelled guns in support, as they approached the Yalu River on the Manchurian border.