In a symmetric war, not targeting civilians is cooperating in an iterated prisoner's dilemma; you don't want to switch from C/C, except in the (seemingly very unlikely) event that the war will end so much more quickly that overall suffering is reduced.

What you say seems correct as a matter of pure terminal values, but this also seems like a great example of a situation where common-sense values that claim to be terminal* are implausible as such but contain real instrumental wisdom.

* to the incomplete extent that common-sense morality makes this distinction