Blackwood was still actively writing during the opening phases of the Great War. He was over forty, so he would not be expected to be called up. His fantasy play The Starlight Express (with music by Elgar) opened in December 1915. It was based on his own novel A Prisoner in Fairyland, and was reminiscent of Barrie’s Peter Pan: it dealt with the astral projections of children’s spirits, which spread good thoughts in the form of stardust. It closed after 40 performances, partly because of the frequency of Zeppelin raids. Elgar cooperated on a gramophone recording of the music. It reached an army officer on the front, who had disliked the gramophone until this, and who wrote to Blackwood: “It is the only means of bringing back to us the days that are gone, and helping one through the Ivory Gate that leads to fairy land or Heaven, whatever one likes to call it” (quoted by Ashley p. 212).
Blackwood had volunteered for ambulance work, and throughout 1916 he expected to be summoned into the Field Ambulance Service. At the end of August 1916 he was called down to Holmbury House in Surrey, the home of William Joynson-Hicks, the chairman of the Belgian Field Ambulance Service. While Blackwood was recovering from his inoculations, which had laid him low, he was asked if he wanted to do secret service work in Holland. He turned this down, on the fairly reasonable grounds that he did not speak Dutch. He could speak French and German, however, and it was suggested that he serve in Switzerland. (Somerset Maugham had worked briefly in this role.)
Blackwood was trained for the job of spy-master, and shown how to recruit agents, to provide them with means of sending reports (using invisible ink), and to make payments: for which he would get 20/- a week plus expenses. He left for Switzerland in early November 1916. He had to do it in secret as it was illegal by Swiss law to work as a secret agent. His base was the Hôtel Bonivard, Territet, just east of Montreux on the shore of Lake Geneva. He used to type his reports in the toilet, so that if he was raided he could claim he was cleaning his typewriter, while flushing the report down the toilet.
He kept up the job for six months. “It was a beastly job. I hated pretending to be someone else, telephoning ‘meet me on Monday at noon’, which actually meant ‘on Tuesday at 6.00’, changing my train at intervals to make sure I was not being followed, and a dozen other schoolboy tricks” (Ashley, p. 222). It is possible he returned to work in Switzerland in late 1917 for a couple of months. He had found a major source of information in “Mrs J”, an English woman whose father had worked with Charles Darwin and who had spent most of her married life in Frankfurt, as a society hostess.
On 15 February 1918 Blackwood started as a searcher for the Red Cross. (On 18 February, John Buchan offered him a job with the Foreign Office, but the offer letter arrived too late.). Blackwood headed off to the British Red Cross Wounded and Missing Enquiry Department at Rouen (the W&M). It was draining work, attempting as it did to find tens of thousand of missing soldiers. The American Red Cross Magazine later published his article about “The Work of a Red Cross Searcher”.
Hilaire Belloc tried to get Blackwood work with the Ministry of Information later in 1918. But instead he was sent to Switerland to contact Mrs J again. (His big coup, Blackwood thought, was uncovering the Kaiser’s homosexuality.) He returned home in October, weeks before the armistice.
Most of this information is taken from Mike Ashley, Starlight Man: The Extraordinary Life of Algernon Blackwood (Constable: London, 2001).