What a fantastic find the War Diary has been. I wasn't aware of such a document until almost a year into the project. After that it became the main source of material to fill in the many blanks left by Harry's letters.
It's quite possible to get a great "feel" for the mood of the times, to appreciate the way that military system worked - and still works - by simply reading through the diaries.
One of the great experiences of this project was to go to to the National archives at Kew and to be handed a box file containing the War Diaries that were actually written by the battalion adjutant a few yards away from Harry. (I kept wondering how they allow me, just me, to handle these precious documents.)
If anyone is undertaking a similar project, then Kew is an important source. Much of the material is available on-line. That's much easier, but in some ways, disappointing, as once the material has been scanned and digitally archived, my understanding is that the originals won't just be handed over to the reader. It is rather special to handle the actual documents.
Anyway, March 1919, the War Diaries stopped. The 9th battalion was broken up and dispersed, with most troops on the way home. Harry, unfortunately had quite a way to go before he managed to get back to Ethel, Willie and Connie.