Service and pension records for more than two million soldiers who fought in the British army in World War I are being put online for the first time.
The documents provide a broad range of detail, from name and next of kin to wounds suffered and conduct record.
The release by the Ancestry website, working in partnership with the National Archives, is taking place in stages over the next two years.
The images are available to view on a subscription or pay-per-view basis.
All the records are already viewable on 28,000 rolls of microfilm at the National Archives in west London, but it is hoped the digitisation process will make them available to a much wider audience.
For an account from a man using newly released documents in a quest to learn more about a grandfather he never knew, see Uncovering the trenches, by Rob Liddle, BBC, Feb. 23, 2007.