212 MILITARY LAW REVIEW [Vol. 216
INHERENT RIGHT OF SELF-DEFENSE
THROUGH THE LENS OF THE 2010 CHEONAN ATTACK
LIEUTENANT COLONEL SANGJAE LEE
A Republic of Korea (ROK) Navy ship (Cheonan), with 104 crew
members on board, sank near the western maritime border with North
Korea after a mysterious explosion on March 26, 2010.1 Forty-six
Korean Navy sailors were killed in this unprecedented tragedy, the cause
of which could not be immediately identified. After a long and thorough
investigation on the cause of the explosion, a ROK-led multinational
investigation team—composed of international experts from ROK,
United States, United Kingdom, Canada, Australia, and Sweden—
concluded that the warship had been sunk by a North Korean torpedo
fired by a submarine.2 Immediately after the investigation report was
completed, the President of the ROK vowed to exercise the right of self-
defense if North Korea attempted military provocation again.3
Academic controversy exists over whether the ROK had a right of
self-defense once it determined that North Korea had perpetrated the
attack. Understandably, due to the gravity and seriousness of the
* Judge Advocate, Army of the Republic of Korea. Presently assigned as Chief of
Military Trial Department, Army Headquarters. LL.M., 2011,. The Judge Advocate
General’s School, U.S. Army, Charlottesville, Virginia,. Masters of Laws (LL.M), 2006,
Korea University at Seoul; Bachelor of Laws (LL.B), 1997, Kyunghee University at
Seoul. Previous assignments include SJA, 50th Division of Korean Army, Daegu, 2009;
Chief of Legal Affairs Department, SROKA, Daegu, 2007–2009; SJA, 32nd Division of
Korean Army, Daejeon, 2005–2007; Military Judge, Zaytun Division, Arbil, Iraq, 2004–
2005; Military Judge, 9th Corps of Korean Army, Jeonju, 2003–2004. Member of the
Korean Bar Association. This article was submitted in partial completion of the Master of
Laws requirements of the 59th Judge Advocate Officer Graduate Course. The author
thanks Major Jeremy Marsh for his inspirational comments on the topic selection. The
author thanks Major Robert Barnsby for his guidance as paper advisor. The author
dedicates this paper to the forty-six fellow sailors who sacrificed themselves while
defending their country. We all know that freedom is not free.
1 MINISTRY OF NAT’L DEF., REPUBLIC OF KOREA, JOINT INVESTIGATION REPORT ON THE
ATTACK AGAINST ROK SHIP CHEONAN (2010).
2 On May 20, 2010, the team presented a summary of their investigation. On September
13, 2010, the ROK government released the final report, reaffirming that it was a North
Korean attack. See id.
3 So-hyun Kim, Lee Says South Will Invoke Right of Self-Defense, KOREA HERALD, May
24, 2010, http://www.koreaherald.com/national/Detail.jsp?newsMLId=20100524000740.
2012] SELF-DEFENSE & 2010 CHEONAN ATTACK 213
incident, the ROK government wanted to conduct a thorough and
objective investigation before assigning a cause. This took considerable
time (fifty-five days), thereby raising the issue of whether immediacy is a
requirement in exercising the right of self-defense.4 In other words, if
immediacy of a military response is required, the right of self-defense
would be difficult to exercise where the aggressor in an attack is not
identified until after a significant period of time has elapsed.
Traditionally, necessity and proportionality are considered to be the
most important criteria comprising the right of self-defense under
international law.5 In addition to these two criteria, some commentators
have argued that immediacy is a separate requirement when exercising
the right of self-defense.6 According to this argument, a response may
not be undertaken in self-defense after a period of time has elapsed since
the armed attack.7 Rather than emphasizing immediacy as a separate
requirement to the exercise of the right of self-defense, timeliness of a
response should only be one of many factors when considering the
necessity of exercising the right of self-defense.
This article explores how the concept of the right of self-defense has
evolved in the field of international law, and also provides the legal
analysis of the criteria of the right of self-defense, traditionally referred
to as necessity and proportionality in Part II. Part III examines the role of
time in the exercise of the right of self-defense. This section focuses on
when the right of self-defense is justified after an armed attack by
analyzing the immediacy issue, concluding that immediacy is not a
separate requirement, but merely one factor in interpreting the necessity
criterion. Part IV then applies that conclusion to the Cheonan incident,
ultimately concluding that the ROK government had the right of self-
defense once it identified the cause of the incident and the aggressor. In
4 In fact, an academic seminar took place in Seoul on 31 May, addressing the legal issues
regarding the Cheonan incident. At this event, Sukhyoen Kim, an international law
professor at Dankook University, argued that it was impossible to exercise the right of
self-defense when considerable time had passed after the armed attack occurred. As part
of his reasoning, he mentions the immediacy principle, arguing that the use of military
force as an exercise of the right of self-defense should occur immediately after the armed
attack. Hongsuk Ahn, It Is Necessary to Fulfill Immediacy and Necessity Criteria to
Exercise the Right of Self-Defense, YONHAPNEWS, May 31, 2010, at A1.
5 YORAM DINSTEIN, WAR, AGGRESSION AND SELF-DEFENSE 208 (4th ed. 2005).
6 See id. at 242.
7 Even though Professor Yoram Dinstein mentions immediacy as one of the requirements
in the exercise of the right of self-defense, he acknowledges two exceptions in the
immediacy principle. See infra note 79.