The Cheonmasan Army (Korean: 천마산대) was an organization that carried out guerrilla warfare among domestically-based armed struggle groups from the March 1st Movement until the 1924.

He later returned to Korea by crossing the Amnok River, gathered his comrades together with Park Eung-baek and others, and officially founded the Cheonmasan Army while declaring himself its commander in March of 1920.

At the time, the size of the army was around 200 members, mostly young and middle-aged men, many of whom were former soldiers of the Imperial Korean Armed Forces which had disbanded after the Battle of Namdaemun in 1907.

)[2][1] Choi Si-heung's army was victorious in many of its engagements, but it also made numerous sacrifices; conventional weaponry additionally limited their capacity in battle.

Their engagements primarily happened along the western mountains and mines in the counties of Uiju, Guseong, Sakju, and Changseong in North Pyongan.

Additionally, Park Jeong-hwan (朴貞煥) organized a base in Subok-myeon (水北面), Sakju County, with several soldiers to raise military funds.

[4] Also in June, several hundred Japanese soldiers invaded through the Saryo Road and attacked the army's main base in Dorongsan (頭龍山).

Of the Cheonmasan Army, Heo Gi-ho (許基浩), Dogo Mu (獨孤武), Lee Chang-geun (李昌根), Ryu Tae-sun (柳泰純), and Oh Won-moon (吳元文) were killed, and three were captured.

Kim Sang-ok (金尙玉) and five others were sent on a mission to gather scattered comrades in Dorongsan, while Park Yeong-chan (朴泳燦) and two others were sent to Chaman-myeon (外南面) to assassinate a Japanese chief and burn down an administrative office.

[4] On June 28, 28 Cheonmasan Army soldiers fought with the 2nd squad for about 40 minutes; 5 people, including Adjutant Heo Gi-ho, were killed.

[4] Conversely, the Japanese attack on the army also intensified, and on June 30, 3rd Platoon Commanders Han Seong-ho and Kim Ok-seon were arrested at Mt.

[2] On August 18, soldiers killed Kawabara (川原英二), the chief of patrol at Wonpung Station, and wounded Fujihara (藤原) in Wonpung-dong, Seosam-myeon.

[2] In March 1921, the Cheonmasan Army was surrounded by approximately 100 Japanese soldiers and subsequently engaged in a fierce battle throughout the day, though there were no casualties.

[4] In late September, the Cheonmasan Army established a camp in the mountains of Anta-ri, Kanggye County, to wait out the winter and prepare to transport provisions.

Afterwards, the Cheonmasan Army attacked the Dongcang garrison in Hwacheon but suffered losses due to issues with terrain.

[4] In early August, Platoon Leader Kim Sang-ok led five subordinates and engaged in a day-long battle with more than 100 Japanese soldiers near Wenjing in Unsan County.

They then received urgent news from Special Envoy Lee Han-jun of the Daehan Gwangbok Army Headquarters, prompting immediate planning for support.

[4] On September 15, the Cheonmasan Army engaged in a battle with the investigation team of the Bukjin Police Station in North Pyongan Province; several soldiers in the opposition forces, including Takamura, were killed.

[2] Later, in order to secure an advantageous base, The Cheonmasan Army moved to southern Manchuria and infiltrated the country through Guanzhen and Ji'an.