There are always three things that I have found keep me going:
1: During the time of intense stess, like when I watched my husband driving in the car ahead of me have a seizure with my daugther in the back seat, I pray. I'm sure you've already found out this one. Even if the prayer comes out something like "Oh Jesus, Oh Jesus Oh Jesus!", we can always remember that the Holy Spirit is there to more or less 'translate' our prayers to the Father.
2: I also sing, either with my mouth or in my head, scripture songs or hymns. One favorite of mine, that you might find encouraging is based upon Psalm 3. You may know it, the words go like this:
Oh Lord, how many are my foes!
Many are rising against me.
Many are saying of me,
There is no help for Him in God.
But Thou, Oh Lord, are a shield about me!
My glory and the Lifter of my head.
I cried unto the Lord,
And He answered me from His holy hill.
This psalm was written by David, who as you probably know, knew something of military pressures.
And 3rd: I'm not sure if you memorize scripture, but when one needs to just be able to calm the mind down, as I'm sure you must at times, reviewing and meditating on memorized Scripture is very calming. There are probably times when you're not able to physically read your bible, but desire the comfort of God's words. Scripture memory is good for times such as that.
One passage you might find encouraging, if you haven't already found it, is 1 Peter 1:6-7:
In this you greatly rejoice, even though now for a little while, if necessary, you have been distressed by various trials, that your faith (being more precioius than gold which is perishable, even though tested by fires) may be found to result in praise and glory and honor at the revelation of Jesus Christ.
I hope this helps, Jon. I don't know if it will be morning or evening when you can next read this, but this is my prayer for you now:
Father, I lift before You Your servant Jon. He is in harm's way, Lord, and yet his mind is on how to better serve You and show his faithfulness to You. Lord, I pray that you give Jon the rest he needs and that You would be his shield, glory, and the lifter of his head. As he desires to share his faith with others, allow him opportunities to show others that his help is in God. Above all, Lord, I ask that you keep Jon safe in the eye of the storm. I ask these things in the name of Jesus, Who will reveal all praise, glory and honor at the appointed time. Amen