The PVA first engaged UN troops on 25 October 1950, with 270,000 PVA troops under the command of General Peng Dehuai, in the Battles of Onjong, Unsan and Pakchon. Following their initial intervention the PVA withdrew, with the UN offensive renewed on 24 November in what was called the Home-by-Christmas Offensive. This triggered PVA to begin another offensive, called the Second Phase Offensive, which pushed the UN forces back in the west while in the east the UN forces were defeated at Chosin Reservoir. The UN forces began a retreat from North Korea and by the end of the year held a line north of Seoul. On the east coast UN forces were evacuated by sea from Hungnam. The PVA launched their third Offensive on 31 December, pushing back the UN forces and recapturing Seoul on 4 January. The UN began a series of counteroffensives beginning with Operation Thunderbolt on 25 January, recaptured Seoul on 16 March in Operation Ripper and advancing the UN lines north of the 38th Parallel in Operation Rugged and Operation Dauntless.