1/5. As a medical orderly during the First World War, Ralph Vaughan Williams acquired a "vivid awareness of how men died". Demobbed in 1919, he began a prolific decade of work, in which the expressive range of his music expanded, and his compositions explored new depths of visionary, mystical ardour. Donald Macleod looks into this hugely significant period for one of Britain's greatest composers. Repeated from Monday at 12 noon