Friday, April 19, 2024

Hiroshima and Nagasaki, a Jus in Bello Evaluation


On 6 and 9 August 1945, the United States used nuclear weapons against the Japanese cities of Hiroshima and Nagasaki, resulting in anywhere from 129,000 to 226,000 deaths[1]. In discussing the ethical status of these events at the conclusion of the War in the Pacific, it is common (perhaps universal?) amongst Just War Theorists to treat the two bombings as a pair, that they were morally equivalent, i.e. the bombings of Hiroshima and Nagasaki were both just or both unjust. Two other possibilities are not mentioned: that the bombing of Hiroshima was unjust but the bombing of Nagasaki was just, or the reverse, that Hiroshima was just but Nagasaki was unjust. These two possibilities are not considered here, subtle and interesting that they may be, and these events will be considered morally equivalent as the jus in bello criteria are applied.

Principle of Discrimination

The Principle of Discrimination presupposes that a distinction exists between people who are threats and those that aren’t, or who are combatants and who are non-combatants[2]. The Principle requires that non-combatants are not to be directly targeted by attacks.

At the time, precision guided weapons were decades away. Also, irregular warfare (assuming terrorist mass-casualty tactics are not employed) is capable of targeted killings (very akin to assassinations) and targeted destruction of infrastructure. America could not wait for precision weapons to be developed, and the War in the Pacific was not an asymmetric war (except for Mao Tse-Tsung's guerrillas fighting the Japanese in China).

The effective discrimination between combatants and non-combatants thus depends on the technology available and the type of war being fought. Evaluation of the use of atomic weapons must be based on those factors.

The targets of the use of the atomic bombs were not chosen to maximize the number of non-combatant deaths. Instead, they were chosen by the Target Committee for their military significance[3]: Hiroshima contained a major military base and embarkation port. Naval ordnance was manufactured in Nagasaki, and that city was also the site of major shipbuilding and ship repair facilities. One proposed target, Kyoto, was rejected because of its cultural and religious significance[4].

Because of all this, the Principle of Discrimination was respected in the use of atomic weapons: the targets were chosen so that facilities relevant to the Japanese war machine would be made unavailable.

Principle of Proportionality

The Principle of Proportionality regarding a particular tactic requires that the value gained by the tactic is "worth" the damaged caused.

No doubt playing in the minds of Americans was the recent (1 April - 22 June 1945) Battle of Okinawa[5]. In this battle, over 150,000 – 260,000 military and civilian personnel were killed on both sides[6]. These numbers are larger than the number of deaths at Hiroshima and Nagasaki combined. Absent use of atomic weapons, the Allies would have to invade the Japanese homeland. That operation, called Operation Downfall, was already under consideration and the number of American deaths were projected to be between 500,000 and one million[7], and that the operation would extend the war at least into February 1947.

It was expected that Emperor Hirohito would surrender following the use of atomic weapons, thus ending the war. If he did not, or if atomic weapons were not used, then the Allied invasion would go forward.

The value gained from the use of atomic weapons was thus the end of the War in the Pacific and the avoidance of what would surely be a costly land invasion. It is reasonable to say that the values gained exceeded the loss of life and damage that the atomic weapons caused.


The bombings of Hiroshima and Nagasaki were evaluated according to the Principle of Discrimination and the Principle of Proportionality. It is found that while non-combatants were indeed killed, the targets were military in nature. Also, the number of deaths caused by the bombings were less than the number of projected fatalities that would result from a ground invasion of Japan. Thus, the use of atomic weapons to end WWII passes the two jus in bello criteria.

Mushroom Clouds over Hiroshima (left) and Nagasaki (right). Photos by George R. Caron and Charles Levy


  1. Clayton Chung, Japan 1945
  2. Helen Frowe, The Ethics of War and Peace
  3. Paul Ham, The Target Committee
  4. Ibid.
  5. Joseph Alexander, The Final Campaign
  6. George Feifer, The Battle of Okinawa
  7. D. M. Giangreco, Hell to Pay


Alexander, J. The Final Campaign: Marines in the Victory on Okinawa. U.S. Marine Corps History Division, 1996.

Chung, C. Japan 1945: From Operation Downfall to Hiroshima and Nagasaki. Osprey Publishing, 2008.

Feifer, G. The Battle of Okinawa: The Blood and the Bomb. Lyons Press, 2001.

Frowe. H. The Ethics of War and Peace: An Introduction. Routledge; 3rd edition, August 25, 2022.

Giangreco, D. Hell to Pay: Operation DOWNFALL and the Invasion of Japan, 1945–1947. Naval Institute Press, 2017.

Ham, P. The Target Committee. Hampress Ltd., 2018.

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