Sadly Ovidio any war is a grim reaper, battlefield casualties in the first 24 hours of the "Battle Of The Somme" Britishicon casualties on that first day were the worst in the history of the British Army, with 57,470 casualties, 19,240 of whom were killed.
I am not sure if this includes MIA or is it after a set period is the soldier who is MIA declared KIA. (Trying to learn more.)