The National Library of Scotland has released scanned images of British Military lists. These give details of officers who served during the First and Second World Wars.
The British Army lists are arranged either by regiment or by officers (in order of seniority), and sometimes both. Some lists include retired officers, and officers of the Royal Flying Corps.
The British Royal Navy lists have alphabetical lists of active and retired officers, and lists of active and retired officers according to role. Includes Royal Marines, Royal Flying Corps, Royal Naval Air Service. Also lists ships and other vessels.
The British Royal Air Force lists have lists of officers arranged according to their role and rank. There are lists of officers in order of seniority, retired officer lists, and alphabetical indexes.
Web site address is: http://digital.nls.uk/british-military-lists/pageturner.cfm?id=97343435