Here, in his own words, is Gwilym Lewis' account, through letters and diary entries, of his experience on the Western Front as a fighter pilot in the Royal Flying Corps/Royal Air Force between 1916 and 1918. (He also put in a stint in England as an instructor.) Lewis also relates his postwar experiences. (He died in December 1996, aged 99.)
I highly recommend this book to anyone interested in reading real-life accounts from the First World War.