Thanks, for your service.
My brother spent the better part of two years in afgan, in the mountains, with a special forces unit. Tough work but much appreciated.
Anyway, to your question.
I think fitday probably over estimate calories burned, but it will be close enough to lose weight. For some it may even under estimate.
You just have to go with what fitday says and see if you lose weight. If you don't and just maintain weight then reduce calories by 10%, if you gain weight drop them by 20%.