The National Archives in the UK have been digitising the British Army war diaries from 1914-1922. These records are the unit war diaries of the British Army in the First World War, not personal diaries (try the Imperial War Museum for those). They are part of a large series of records which contains many more diaries scheduled for digitisation, and the NA are now conserving, sorting, digitising and itemising thousands more diaries from the WO 95 series as part of their First World War 100 programme.
The digitised diaries cover activity in France and Belgium. The amount of detail each Unit Diary contains varies quite a bit. Some diaries only record daily losses and map references whilst others are more descriptive, with daily reports on operations, intelligence summaries and other material. Some refer to maps and plans which were regarded as confidential and removed from the diaries before they were preserved. A few diaries contain details about awards of the Military Medal and the Meritorious Service Medal, but mostly they do not contain a great deal of information about specific individuals. Many of the war diaries were scribbled hastily in pencil and use obscure
abbreviations, whilst some are the second carbon copy of the original,
so they may be difficult to read.
The diaries include those of 247 First World War hospital camps, hospital ships, convalescent hospitals and veterinary hospitals. These war diaries reveal different methods of treating injured and disabled soldiers, and give insight into life in hospital during the First World War and the daily routines, operations and special events. These even include Christmas services: on board Hospital Ship Vasna in December 1918, ‘a generous supply of gifts were obtained from the Red Cross Depot in Basra and were distributed by the Matron to all patients, passengers and staff.’ They also illustrate the challenges involved in setting up hospitals in battlegrounds and at sea, and the logistics of nursing thousands of soldiers and animals back to health. The war diary for HMHS Erinpura reveals that in just 15 voyages in 1918, the ship had carried ‘6126 sick and 4067 troops’.
You can search by Regiment, Battalion, Brigade or Division (number), but keep in mind that if you search only by regiment, your search results will include all the battalions in that regiment. PDF files of the diaries can then be downloaded. With each download, you will typically see a unit diary that may cover a period of several years and may be divided into several PDF files. You can then scroll through the PDF files to locate the battalion and dates that you are interested in. Note that while searching is free, there may be a charge to download documents.