Do any Christian versions of 'Just War Theory' address cases in which foes exploit the principles of Just War to their own advantage?

The Bible tell us how to make war - justly. We can also learn from other thinkers: *

Weapons are terrible things – and no sage will have anything to do with them, unless there is no alternative.*

Tao Te Ching *

Outside the storms of war may blow and the land may be lashed with the fury of its gale, but in our own hearts this Sunday morning there is peace. Our hands may be active but our consciences are at rest . . . We are fighting to save the world from the pestilence of Nazi tyranny and in defense of all that is most sacred to man.*

Winston Churchill, September 3, 1939

From the earliest times man fought wars, sometimes to plunder, sometimes to take women and other times to take over land. After money (gold) became part of civilization, tributum aut bellum (tribute or war) became a common demand between nations. These were economical reasons for war and to them were added many other reasons - some good, some less clear. However, no matter what the reasons were, the common bond between all wars is that each of the various parties involved in the war claimed that they were fighting a ‘just war’. The claims were more often than not based on religious grounds implying that they were fighting a ‘just war’ while the other side was not. Very few (if any) participants in a war have ever gone into the war claiming that their cause is evil and unjust. The incredible conclusion is therefore that all wars are just or alternatively, that all wars are unjust.

In 990 CE, rules and regulations for war were issued by the Pope that was known as pax dei, the ‘Peace of God’. War was considered just if it was fought for ‘liberty’ and ‘freedom’ without coming to grips with what ‘liberty’ or whose ‘freedom’. The law was intended to protect women, clerics and peasants, livestock and other means of making a living. The basis was laid for thinking that there is such a thing as a ‘just war’. This became horribly twisted during the Crusades and Christian scholars and leaders, including popes, started wondering how wars that have such horrific results could be called ‘just’. The task of trying to make sense of this fell to Thomas Aquinas (1224 – 1274) whose thinking determined the doctrine of the Roman Catholic Church and later all the Christian groups, and lately it has seen a revival in the thinking of a widely diverse group of people outside of religion. Thomas constantly worked on the principle that truth can be arrived at by blending human knowledge or facts with spiritual “feeling” (religion). Thomas believed that when what was seen as right (knowledge) and what was felt as right (religion) were the same, there was an absolute right.

The ‘just war’, according to Thomas, had to be jus ad bellum, meaning there had to be morally sound reasons for the war and it had to be jus in bello, meaning it had to conducted in a moral manner. A morally sound reason for a war had to include both a legitimate factual reason and it had to promote the cause of ‘good’; both fact and feeling has to be present. To Thomas’ original ‘just cause’ for war other thinkers have added that there had to be no other options open as alternatives to war, that war must only be conducted to the degree or proportion needed, and that the war will bring more benefits than wrongs. ‘Just wars’ have also been seen as wars to end wars, wars in self-defense, war to right previous wrongs and wars to punish offenders.

Thomas emphasized that a war can only be jus ad bellum if it is also jus in bello and later thinkers added that it also had to be jus post bellum, that is that there is moral conduct after the end of the war. Right conduct in war includes what weapons can be used, conduct towards civilians and POWs and what is and is not legitimate targets, while moral conduct after the war covers about the same topics at the end of hostilities. What Thomas (and later thinkers) did was to remove the doubts felt during the Crusades by creating a moral foundation for the concept of a ‘just war’ and thereby legitimizing war based purely on human knowledge and feeling.

Jus ad bellum has resulted in more, and more terrible, wars as it allowed people to act without having to take personal responsibility.

A war can only be jus in bello if the soldier follow the Bible and particularly:

When thou takest the sum of the children of Israel, according to their number, then shall they give every man a ransom for his soul unto the Lord, when thou numberest them; that there be no plague among them

Exodus 30:12

And we have brought the Lord’s offering . . . to make atonement for our souls before the Lord.

Numbers 31:50 This brings about the correct code of behavior.

Before the battle, the soldiers ransom their souls from God. The word ‘ransom’ as it is used here is always used in the context of the taking of a human life in circumstances that does not constitute murder – that is through carelessness (accidents are something completely different). The person cannot be charged with murder but he acknowledges responsibility for the act that led to the loss of life. The difference is that here the ‘ransom’ is paid in advance. The soldier is not a warrior of God that can act with impunity like the Crusaders. He takes his soul from the protection of God into his own hands and takes responsibility for it and afterwards must prove jus in bello not only to humans but also to God. God will forgive him if he behaved in a morally correct manner and makes atonement afterwards for the killing done as acts of war. He cannot make atonement before the time and there is no atonement possible for any misdeeds.
(It additionally include a responsibility towards the self, and other soldiers.)

For the religious soldiers correct conduct in war is a religious obligation. A religious machine-gunner that removes the gun-belt during a patrol because it is uncomfortable resulting in his own death is responsible for this act with his soul - he had committed suicide. If his negligence results in the death of others, he had committed murder in the eyes of God.

Personal correct execution is required so the soldier’s acts do not result in the slaughter (‘the plague’) of others. Bravery is required for the sake of the soul, and so is not making mistakes.

With a threat as severe as Christianity is facing now, placing restraints on commanders and soldiers that limit their ability to function to the maximum extent of their abilities both strategically and tactically, is difficult to justify. But, the 'purity of arms' must go beyond what most military does in order to place a 'fence' around jus in bello and so ensure the souls of the soldiers.

Summary: No, the Just War doctrine is not intended to provide guidance at this level of detail.

First a brief summary of what the Just War Doctrine is. It's intended to be an answer to the question of whether a Christian can morally fight in a war, and the very brief summary is: "A Christian can fight in a war, as long as it is 'Just'". Many Christian groups hold to this view, with the main alternative positions being the Pacifist one, which says that a Christian can never fight in a war, and the one that says that a Christian can and should fight if ordered to do so by a secular authority.

The doctrine also provides some guidelines for when a war is considered 'Just'. There are two main parts to that. The first is when a war may justly be begun - for example it must not be a war of aggression, it must be fought by a legitimate authority, and only if all other means have been exhausted. The second is the conduct of the war: for example it should be a proportionate response to the evil the war is intended to prevent, and it should involve only what is militarily necessary to achieve its objectives.

The first rules for a Just War were set out many hundreds of years ago, including those of Thomas Aquinas (1225-1274) and Stanisław of Skarbimierz (1360-1431). While there have been variants on these rules, the approach has always been to set out principles rather than to prescribe detailed responses to specific situtions. The principles has been applied to wars from the bow-and-arrow era to that of nuclear weapons.

Because of the level at which they are laid down, it makes little sense to try and address specific situations that have arisen only in the last few decades. It is also worth mentioning that none of the forumlators of the Just War guidelines intended them to be applied only in cases in which the other side also 'played by the rules', and it's widely believed that "do good to other people only when they are being good to you" is foreign to Christian belief. Medieval warfare, the norm when these rules were being set down, was at least as nasty as modern 'asymmetric' warfare.