The entire town of Haean-myeon is contained in Haean Basin. Also known as Punch Bowl, Haean Basin is surrounded by high peaks and one of these peaks is Gachilbong.

The nature of the terrain in the Gachilbong area made it difficult to conduct military operations during the Korean War. The North Korean military utilized these natural features to build a solid defense position and launch counterattacks, while the South Korean soldiers in the lowland were in a disadvantageous position. South Korean soldiers were under the command of 5th Division Commander Brigadier General Min Gi-sik and 24th Regiment Commander Colonel Yu Ui-jun. On the North Korean side, the 7th, 14th, and 32nd Regiments of the 27th Division and the 23rd Regiment of the 12th Division under the 2nd Corps fought back.

By sending a military deployment and conducting search operations, the South Korean military completed a reconnaissance of the area on August 30 and advanced to counterattack. On August 31, after defending their position for two days, the South Korean soldiers were able to break the North Korean resistance. Each unit secured a strongly fortified position to draw the North Korean soldiers out. Thereafter, South Korea launched an all-out attack and captured Hill 1241. However, North Korea attacked again and South Korea retreated. After several attacks and counterattacks, South Korea was able to take back Gachilbong and the surrounding areas. Although it resulted in heavy casualties on both sides, this battle ultimately gave South Korea possession of Haean Basin.