The diary, thought to have been written by an officer of the Third Battalion Northumberland Fusiliers, is to go under the hammer at Bellmans Auctioneers in Wisborough Green on April 10.
It includes diary entries and copies of his letters home, and covers the period August 1914 - June 1915, when the Battalion - as part of the 9th Infantry Brigade - were engaged in the first Battle of Ypres.
It presents a detailed daily account of harrowing warfare. The diarist saw comrades killed in front of him, endless mud and rain, yet elements of his humour manage to shine through; “billeted at Rosendaal Chateau, whole place shelled to pieces … had very fine Louis XV chairs to sit in and lovely china … a strange contrast!”
On the Front Line, he notes that “in one place the [soldiers] have a sort of understanding, and show their heads over the top … when the Germans get word from their gunners our trenches are going to be shelled, they sign over to us, and the Brits do the same. General HQ would be pretty sick if they knew this”.
Bellmans books specialist Denise Kelly said: “This incredible diary is so full of detail. I could not put it down, and turning the pages I was instantly transported back to the trenches, as if I was standing next to the writer.
“I experienced the close bond and trust between the officer and his men, I felt the cold, endless rain and horrific mud, I heard the endless noise of shelling and gun fire, realising very quickly why the life expectancy of these men was so short.
“I have no idea how the writer survived as long as he did as I despaired reading endless names of his comrades falling to snipers, being shelled or missing.
“This is a fascinating, moving, historical record of horrific battles fought by very brave men”.
The diary is expected to sell for between £400-£600.