Soldiers who died in the Great War and have no known grave.

Those Great War soldiers who died in the Hell of No-Man's-Land during attacks, would have lain where they fell until;

a] there was a truce or

b] the ground was taken - perforce left where they fell in both cases until that burial details of either side could reach the corpses safely. Or

c] - until the pitiful remains were either buried or blown to pieces by artillery bombardments. In the first two instances, even if the Dead were recovered and buried "near the Front line", if the burial was later subject to artillery bombardment, or subterranean mining, the explosions might have exhumed the corpses, fragmented the remains, and buried them again yards from their original positions,   so that subsequent Burial Teams could not locate any remains at all.

Research seems to indicate that as far as Corpse Identification went, any of the following might happen, again according to circumstances............

i] a soldier's surviving comrades might have the time to grab his ID tag and papers at the time of -  or shortly after -  his death - to deliver them up to their Company Officer; - but only if they, themselves, survived the attack

ii] If the corpse was recovered by a Burial Detail, the Detail would thoroughly search the body, and it's equipment for any signs of Identity  to report name and location of the body to Higher Authority, before formal burial. If circumstances permitted, such burials were usually given some kind of wooden grave marker , with an ID plate often stamped out of tin nailed to the wooden post, plank, or cross. However, in such burials associated with re-fought-over ground, the pressures of combat meant "enemy" dead got less care and respect than one's own.

iii] One must not forget, however, that such burials "in the Line" might also be in ground fought-and-refought-over more than once, - and in the process, the wooden markers too, might be destroyed by artillery bombardment. In which case, subsequent Grave Registration Teams, on rediscovering the Remains at a later date,  would almost certainly be faced with decaying corpses from which all personal identification - ID Tags and papers - had already been removed by the original Burial Party.  If any of the equipment also in the grave had a soldier's regimental Number stamped into it, or written on it, a positive ID could still be made, - but if none of these marks nor rank markings had survived, the Reburial Team might be able to do no better than identifying a Regiment from the metal badges and/or buttons.

iv] One must also come to terms with the fact that after the War, the entire Western Front was declared a "Zone of Total Destruction", - and during the monumental clear-up, many "lost" and once-buried soldiers were found, and exhumed, and laid to rest again, with others of the Fallen in large "Cemeteries of collection", often some distance from where they may have died, and been subsequently found. There were tens-of -thousands of such re-burials.  No matter how much care was applied to such exhumations and reburials, during the process there was a very real possibility for identity clues to be lost. In the years immediately after the Great War, if human remains were found by French or Belgian civilian "clear-up " personnel, - there is no guarantee that the civilians would have taken the same time and trouble to identify human remains, before handing them over to the nearest Military Authorities, as military Graves Registration Teams might have done.

v] And finally, there were areas of the battlefront which had been so saturated with munitions that - after a number of accidental post-War deaths amongst Graves Registration Teams, the Authorities regretfully decided that such areas could not be safely searched any further for corpses, and must be left undisturbed, and have been to this day.

For example, I was told that both High Wood and "Devil's" [Delville] Wood on the Somme are such "do not disturb" areas. In such areas, today's French and Belgian "Deminage" teams have calculated the Unexploded explosives,  shells,  mines,  ammunition content, could be as high as 2 TONNES/sq, M

As to the question how long would a body last in the ground for ID to be possible?

That depends on a number of factors, and would vary from section to section of the Western Front. When the new motorways were being driven through the old Front Line during the 1970's, the Construction Crews discovered a number of deep-dug bunkers in the chalk, their entrances   "blown-in", still containing the mummified remains of their German defenders. But in the wet country of Flanders, putrefaction and total decay of all soft tissue and cloth organics might well be very fast, depending on the chemical contents of water and soil. First of all, however, don't forget the plague of millions of rats mentioned in so many Great War battlefield memoirs. However, if the burial seemed undisturbed, and the remains have become totally skeletonised, even with the uniform quite rotted away, none-the-less Identity clues could come from buttons, belt buckles, Unit badges, and items of kit carrying Regimental numbers. Three such cases come to mind –

1] the well-past-WW2 discovery and identification of the remains of John Kipling, the son of the famous Author; missing in action in WW1; -

2] the identification of the "lost" grave of the WW2 German Tank Ace Michael Wittman and his crew; - missing in action during the savage fighting in Normandy; -

3] and the discovery and identification of the remains of Squadron Leader Adrian Warburton, the famous "lost in his P38Lightning on a mission over Germany" RAF Photographic Reconnaissance Ace. All have been re-buried with full military honours.

WW2, - when they too, could be persuaded to talk about it, - which was rarely. When we consider that situation in relation to soldiers KIA, the wonder and the pity of it all - is that so MANY buried on the
Battlefield were eventually identified and laid to rest with Honour, until The Judgement; and that so few - relatively speaking, have no known graves.