 Operation Commando finally ended on 15 October with the US I Corps having successfully seized the Jamestown Line and destroying elements of the 42nd , 47th , 64th and 65th Chinese Armies . Chinese losses were estimated at 21 @,@ 000 casualties , while UN losses were 4 @,@ 000 — the majority of them in the US 1st Cavalry Division which had borne the brunt of the fighting . Although a few hills south of the line remained in communist hands — requiring a follow @-@ up operation known as Operation <unk> which succeeded in capturing these positions by 19 October — UN supply lines near Seoul were now free from Chinese interdiction . With the peace @-@ talks ongoing , these operations proved to be last actions in the war of manoeuvre , which had lasted the previous sixteen months . It was replaced by a static war characterised by fixed defences , trench lines , bunkers , patrols , <unk> parties and minefields reminiscent of the Western Front in 1915 – 17 . Construction of defensive localities began almost immediately , although such operations were confined to the reverse slopes during the day due to artillery and mortar fire which made such operations hazardous . Patrolling forward of the Jamestown Line also began in order to prevent the Chinese from gaining control of no <unk> land . Yet even as the war became a contest of positional warfare and <unk> , growing western political <unk> ensured that UN commanders were increasingly <unk> of limiting casualties . 
