The First Battle of Maryang San ( 3 – 8 October 1951 ) , also known as the Defensive Battle of Maliangshan ( Chinese : 马良山防御战 ; pinyin : Mǎliáng Shān Fángyù Zhàn ) , was fought during the Korean War between United Nations ( UN ) forces — primarily Australian and British — and the Chinese communist People 's Volunteer Army . The fighting occurred during a limited UN offensive by US I Corps , codenamed Operation Commando . This offensive ultimately pushed the Chinese back from the Imjin River to the Jamestown Line and destroyed elements of four Chinese armies following heavy fighting . The much smaller battle at Maryang San took place over a five @-@ day period , and saw the 3rd Battalion , Royal Australian Regiment ( 3 RAR ) dislodge a numerically superior Chinese force from the tactically important Kowang @-@ San ( Hill 355 ) and Maryang San ( Hill 317 ) features , in conjunction with other units of the 1st Commonwealth Division .