Operation Thunderbolt, also known in China as the Defensive Battle of the Han River Southern Bank was a US offensive during the Korean War.
It represented the first offensive under the new commanding officer of the 8th US Army, General Matthew Ridgway. It started less than three weeks after the Chinese Third Phase Campaign had forced UN forces south of Seoul.
Thunderbolt was preceded by Operation Wolfhound, a reconnaissance in force by the 27th Infantry Regiment ‘Wolfhounds’ that began on 15 January 1951. At this time the Chinese forces in the central sector were still in possession of Wonju and a full assault could not be made until this sector was under US control. Thunderbolt itself began on the 25 January, when troops of I and IX Corps advanced from the western sector of the front northwards towards Seoul.
This attack was heavily supported by artillery and air support, in accordance with Ridgway’s policy of attrition by superior firepower against a numerically superior foe. By 9 February, the offensive had reached the Han river with the rest of the Chinese defenders retreating to the north of Han River by the end of February.
X Corps, once again part of the 8th Army, held the central sector and moved forward as Operation Roundup on 5 February. Responding to the UN advances, Chinese forces under Peng Dehuai then counter-attacked as the Fourth Phase Campaign, achieving initial successes at the Battle of Hoengsong.
Chinese forces were later held off at the Battle of Chipyong-ni and the Third Battle of Wonju. The concentration of firepower and reliance on close air support in the face of large numbers of light infantry employed here would later become an influence on US doctrine during Vietnam.
Thunderbolt was followed almost immediately by the second UN counter-offensive, Operation Killer.
*For more on this subject see the full article for Operation Killer at Wikipedia.org.