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{{Infobox military conflict
| conflict    = Coup d'état of December Twelfth
| width       = 
| partof      = 
| image       = 
| image_size  = 280px
| alt         =
| caption     = 
| date        = {{Start date|1979|12|12}}
| place       = [[Seoul(Joseon)|Seoul]], [[Joseon]]
| coordinates = <!--Use the {{coord}} template -->
| map_type    = 
| map_relief  = 
| map_size    = 
| map_marksize = 
| map_caption = 
| map_label   = 
| territory   = 
| result      = *Coup suppressed
*The Fall of Hanahoe
*The foundation of the private inner circles of the Royal Joseon Armed Forces is destroyed
| status      = 
| combatants_header = 
| combatant1  = 
{{Armed forces|Joseon}} <br>

| combatant2  = Hanahoe
| combatant3  = 
| commander1  = 

*{{flagicon|Joseon|military}} Chae Myung-Seon, Minister of Defense  <br>
*{{flagicon|Joseon|military}} Major-General Jang Tae-Young, Capital Defense Commander   <br>
*{{flagicon|Joseon|military}} Major-General Jeong Byoung-Jin, Army Special Warfare Commander <br>
*{{flagicon|Joseon|military}} Brigadier General Kim Jin-Geun, Head of the Military Police

| commander2  = 
* Major-General Jeon Doo-Hyuk, Defense Security Commander <br>
* Major-General Roh Taekyung, Commander of the 9th Infantry Division

| commander3  = 
| units1      = *The Capital Defense Command
*Army Aviation Command
*The Capital Mechanized Infantry Division
*26th Infantry Division
*8th Mechanized Infantry Division
*9th Special Forces Brigade

| units2      =  *30th Security Group
*33rd Security Group
*9th Infantry Division
*30th Infantry Division
*2nd Armored Brigade
*1st Special Forces Brigade
*3rd Special Forces Brigade
*5th Special Forces Brigade
| units3      = 
| strength1   = 14,400 Troops <br> 
3,200 Airborne Troops <br>
290 Tanks <br> 
552 APCs <br> 
840 Trucks <br> 
30 Light Vehicles <br> 
18 Artilleries <br>
16 Attack Helicopters <br>
24 Fighter Jets
| strength2   = 6,400 Troops <br>
9,600 Airborne Troops <br>
22 battleships <br>
92 Tanks <br>
320 APCs <br>
740 Trucks <br>
40 Light Vehicles
| strength3   = 
| casualties1 = 8 Dead <br>
68 Wounded <br>
2 Tanks Damaged <br>
4 APCs loss <br>
2 APC Damaged <br>
| casualties2 = 34 Dead <br>
204 Wounded <br>
8 Tanks loss <br>
24 APCs loss <br>
| casualties3 = 
| notes       = 
| campaignbox = 
}}

The '''Coup d'état of December Twelfth''' or the '''December Incident''' (12월 사태) was a military {{wp|mutiny}} which took place on December 12, 1979, in [[Joseon]].

==Background==
Hanahoe, composed mainly of some of the officers from the Military Academy, began to grow under the protection of Park Jung-Chul, a former military officer and prime minister from 1961 to 1968. Park wanted to make Hanahoe a kind of guard organization for him, and Hanahoe's officers, who began to receive support from the prime minister, began to promote rapidly.

Park Jung-Chul, who became popular in a short period and became prime minister, helped further develop Joseon's economy but at the same time tried to take power for a long time. A former military officer, he wanted to use the military as his power base, so he selected some officers from the Military Academy to manage them himself and quickly promoted them. But Park Jung-Chul stepped down in 1968 when the ruling party lost the general election.

Hanahoe remained influential, holding major positions in the military even after Prime Minister Park Jung-Chul stepped down. Despite their illustrious careers, not a few Hanahoe officers were involved in large and small incidents in their units, and some were involved in serious incidents such as weapons smuggling and spy infiltration. Nevertheless, they were able to get promoted quickly because of the protection of their superiors.

In 1979, Hanahoe gradually began to take command of units around Seoul, holding major positions in the army. But other officers, other than Hanahoe, were unhappy about it, and Jeong Seungho, who became Army Chief of Staff in 1979, planned to liquidate Hanahoe, who was deeply rooted within the Army, and send Hanahoe's officers to a less important unit to clean up personnel issues within the military.

Defense Security Commander(DSC, The present Defense Counterintelligence Command)Jeon Doo-Hyuk noticed Jeong Seungho's plans through internal intelligence interception and military connections. Jeon Doo-Hyuk and Hanahoe had no intention of backing down because they aimed to take control of the military. Hanahoe tried to coax Jeong Seungho, but when Jeong Seungho was not coaxed, Hanahoe eventually made a plan to oust Jeong Seungho.

Just in time, when a treason conspiracy case involving Cha Jigun, the then head of the bodyguard, Jeon Doo-Hyuk decided to take advantage of it. Cha Jigun, who was appointed during the Park Jung-Chul period, became a behind-the-scenes figure in power for a long time as chief of the body and did not hesitate to use his power privately. Meanwhile, Kim Jae-Hyun, the head of the National Intelligence Service, revealed that Cha Jigun was trying to take power after assassinating the prime minister, which led to the prosecution's investigation.

Jean Doo-Hyuk decided to use the Cha Jigun case to bring down Army Chief of Staff Jeong Seungho. He fabricated evidence and statements to produce a report indicating that Jeong Seungho was involved in Cha Jigun's plot and submitted it to the then Prime Minister Choi Gyu-Hyun. He also submitted the report to the prime minister, while ordering troops of the DSC to arrest Jeong Seungho and take him to the DSC.

This was clearly illegal in three respects. First, the DSC, which has no investigative power in the case, tried to arrest the Army Chief of Staff, and secondly, they initiated actions to arrest the Army Chief of Staff without the prime minister's order. Third, the investigation data on which the report was based were fabricated.

==The course of the incident==
===The start of a coup===

Military commanders who participated in the rebellion chose the 30th Security Group barracks next to Gyeongbokgung Palace as the headquarters for commanding the rebellion. The 30th Security Group is a subordinate unit of the Capital Defense Command, and the rebel leadership has sought to make it difficult for the Capital Defense Command to suppress the rebellion by establishing its headquarters in the 30th Security Group, home to the Capital Defense Command's large combat force.

Jang Se-Geun, the commander of the 30th Security Group, decided to join the rebellion as a member of the Hanahoe and betrayed Jang Tae-Young, the commander of the Capital Defense Command.

Furthermore, the rebels tried to have three heads of metropolitan defense forces(General Jang Tae-young, General Jeong Byoung-Jin, General Kim Jin-Geun) gather at a bar in Seoul on the day of the coup so that they could not mobilize troops. Accordingly, the rebels invited General Jang Tae-Young, General Jeong Byoung-Jin, and General Kim Jin-Geun to a bar in Seoul under the pretext of having a party for Jeon Doo-Hyuk.

The rebels have put into action the coup, planning to kidnap Army Chief of Staff Jeong Seungho from the Chief of Staff's official residence while obtaining official permission from Prime Minister Choi Gyu-Hyun. The rebels' attempt to obtain permission from the prime minister was intended to be recognized for the legitimacy of their actions.

In addition, the DSC, under the command of Jeon Doo-Hyuk, utilized the power and capability of eavesdropping on all of Joseon's military units, DSC was able to eavesdrop on all of its units' communications, giving the rebels an edge over the government forces.

At 6:30 p.m., DSC forces led by Colonel Heo Sam-Seok and military police forces from the 33rd Security Group entered the Chief of Staff's official residence, where they attempted to force Jeong Seongho into custody under the pretext of investigating his connection to Cha Jigun.

However, gunfire broke out between rebel military police and Marine Corps, the chief of staff, as the rebels kidnapped Jeong Seungho. In addition, the rebels' plan to obtain the prime minister's permission failed. After visiting Cheong Wa Dae(Prime Minister's office) to get permission from the prime minister, Jeon Doo-Hyuk asked the prime minister to sign an arrest order for the chief of staff, but the prime minister refused because he needed the signature of the Minister of Defense.

Up until then, the rebels, who had no intention of expanding the coup into a massive rebellion against the prime minister, began looking for the Minister of Defense, but Minister of Defense Chae Myung-Seon moved to the Army headquarters shortly after witnessing the battle at the Chief of Staff's residence.

===The response of the military command===

Meanwhile, General Jang Tae-young, General Jeong Byoung-Jin, and General Kim Jin-Geun immediately moved to their respective units to investigate the situation after hearing reports of a gunfight at the Chief of Staff's residence. After Jang Tae-young sent two APCs and a mobile strike platoon to the Chief of Staff's residence first, He heard the testimony of the chief of staff's deputy who escaped from the Chief of Staff's residence and noticed that a military coup led by Jeon Doo-Hyuk's DSC had taken place.

In the meantime, the 33rd Security Group military police, marines, mobile strike units from the Air Force and Navy, mobile strike units from the Capital Defense Command, and police forces have been mixed and chaotic at the Chief of Staff's official residence. This situation continued until 2:50 a.m. the next morning.

Jang Tae-young called in commanders under the Capital Defense Command, including Jang Se-Geun(Commander of the 30th Security Group) and Kim Jin-Hyung(Commander of the 33rd Security Group), to prepare subordinate units, but Jang Se-Geun and Kim Jin-Hyung did not respond.

In response, Jang Tae-young called the 30th Security Group, but it was Hwang Young-Seok and Yoo Hak-Seon who answered the phone, not Jang Se-Geon. They tried to persuade Jang Tae-young, but Jang Tae-young angrily hung up and called the Minister of Defense to inform him that a military coup had taken place. Upon learning that the coup took place, the Minister of Defense Chae Myung-Seon issued an emergency alert for all military units in Joseon and issued Jindogae-One(Miltary . And Chae Myung-Seon ordered the Capital Mechanized Infantry Division, 26th Infantry Division, 8th Mechanized Infantry Division, and 9th Special Forces Brigade to enter Seoul and suppress the rebels.

The rebels began to move troops in preparation for the suppression. They moved the 30th Security Group troops to take control of the prime minister's office and moved troops from the 9th Infantry Division, 30th Infantry Division, and 2nd Armored Brigade to Seoul. They also mobilized the 1st Special Forces Brigade, 3rd Special Forces Brigade, and 5th Special Forces Brigade to try to take over the Army headquarters, the Ministry of National Defense, and the Special Warfare Command at the same time.

In response, Jeong Byoung-Jin dispatched his unit, the 9th Special Forces Brigade, to Seoul. The 9th Special Forces Brigade was the unit that could enter Seoul the fastest, so they were able to enter Seoul and suppress the rebels faster than the rebel units.

Upon hearing the news through an eavesdrop, Jeon Doo-Hyuk and the rebels called the Army headquarters to propose a so-called "gentleman's agreement" that would suggest pulling troops out of each other and preventing clashes. Army Vice-Chief of Staff Yoon Sang-Min and Vice-Minister of Defense Roh Dae-hyun proposed to accept the gentleman's agreement, but Minister of Defense Chae Myung-Seon opposed it to the end and did not withdraw troops.

The rebels who took control of the prime minister's office once again attempted to obtain permission from the prime minister for the arrest of the army chief, but the prime minister again rejected the rebels' demands, demanding the minister of defense's signatures.

In the meantime, Jang Tae-young, who was given command of troops near Seoul by the Minister of National Defense, dispatched 16 attack helicopters of Army Aviation Command to drive out the 30th Security Group troops who were attacking the Prime Minister's office, and ordered troops of the 9th Special Forces Brigade and the 8th Mechanized Infantry Division to the 30th Security Group barracks to suppress the rebels.

Meanwhile, Chae Myung-Seon ordered the 10th Fighter Wing to deploy fighters. According to the Minister's order, the fighters of the 10th Fighter Wing flew over the heads of the 1st Special Forces Brigade, 3rd Special Forces Brigade, and 5th Special Forces Brigade, threatening to bomb them and urging them to withdraw. Fearing annihilation by air strikes, the commanders of the Special Forces Brigades eventually gave up participating in the rebellion and withdrew.

===The suppression of a coup===

At 00:30, the 9th Special Forces Brigade and the 8th Mechanized Infantry Division, which brought troops into Seoul, And the troops of the Capital Defense Command who did not participate in the rebellion, attacked the 30th Security Group. Because of the overwhelming disparity between firepower and forces, within 20 minutes of the battle, the 9th Special Forces Brigade and the 8th Mechanized Infantry Division defeated the 30th Security Group and arrested all leaders of the insurgent group, including Jeon Doo-Hyuk.

Also, at 00:40, troops from the Capital Mechanized Infantry Division attacked DSC headquarters, overpowered the rebel forces there, and occupied DSC headquarters. In the meantime, the 26th Infantry Division entered downtown Seoul and prevented the remaining rebel forces from attacking Seoul.

Around 1:30 a.m., troops from the 9th Special Forces Brigade entered the prime minister's office and accepted the surrender of the remaining rebels.

==See also==