With the outbreak of war, on 5 August 1914, Smith-Barry was appointed as a flying officer. Only days later, on 14 August, while on operations in France with
No. 5 Squadron RFC, Smith-Barry's
Royal Aircraft Factory B.E.8 had an engine failure and crashed, killing his passenger. Smith-Barry had had two broken legs but on hearing of the imminent arrival of Germans he managed to get back to England on his own accord. and less than a month later on 1 December his temporary promotion was made permanent. 3 July 1916 saw Smith-Barry temporarily promoted to major. On 23 August 1917 he was made a wing commander and temporary lieutenant-colonel. Towards the end of January 1918, he was promoted to the temporary rank of
brigadier-general but he relinquished the rank on 23 February 1918. Later in 1918, his promotion to colonel in the new Royal Air Force was gazetted but this was later cancelled. He was awarded the
Air Force Cross in May 1918. ==Later years==