Josh 8:2

“Inasmuch as God ordered Joshua to plant an ambush in their rear, that is, to plant warriors in hiding to ambush the enemy, we can learn that such treachery is not unjustly carried out by those who wage a just war. Thus, a just man, if he wishes to undertake a just war, ought to think chiefly in these matters about nothing else than whether it is right for him to do so, for it is not lawful for everyone to wage war. However, once he has undertaken a just war, it makes no difference to the justice of the war whether he wins in open warfare or by treachery. However, those just wars ought to be defined as those which avenge injuries, if the tribe or state which is about to be sought in war, either neglected to punish a crime improperly committed by its own countrymen or neglected to repay what had been lost through those injuries. Moreover, without doubt that type of war is just which God commands, since there is no iniquity in him and he knows what ought to be done to each person. In this type of war the general of the army or the people themselves are not to be deemed so much the instigator of the war as much as its agent.Joshua sent thirty thousand warriors to vanquish Ai.… We must consider whether every attempt at deception ought to be reckoned as a lie and, if so, whether a lie can be just, when someone who should be deceived is deceived. And if not even this kind of a lie is found to be just, we must still relate what transpired with the ambush to the truth with some other meaning.”