Jenny and I have used this prayer on Memorial Days past (it would also be suitable for Veterans Day). It has been heavily redacted and I no longer remember where it originally came from.
Righteous God, who rules the nations. We pray to you to guard the brave men and women who risk themselves in battle for their country. Give them compassion for enemies who fight for their own patriotic causes. Keep them from the hate that hardens, from scorekeeping with human lives and preserve them from the sins peculiar to war.
Though they must be at war for a time, let them live for peace, as eager for agreement as for victory. Strenthen them as they encourage one another, and never let hard duty separate them from loyalty to your Son, our Lord, Jesus Christ.
We pray for those who have sacrificed themselves, giving their lives for the sake of others. We pray that we might hold them all in continual remembrance, and ever think of them as with you in that city whose gates are not shut by day and where there is no night.
Finally, we seek your forgiveness for the times when we have sent our brave men and women into battle unnecessarily. Embolden us by your grace that we might work for a world where fear has been dispelled and the nations are at peace. Amen.