To devotees of Tolkien, the trench fever that led to his repatriation from the Western Front in November 1916, was a fortuitous circumstance that saved an extraordinary intellect from annihilation in the mud and blood of French or Belgian fields. His return is widely seen as an escape to the peace and quiet of treatment and convalescence in England. Yet his posting to Holderness, in April 1917, placed him in the alarms and excursions of another front line. This article examines the background to Tolkien’s military duties in the East Riding of Yorkshire from April 1917. The night bombing raids on England by Zeppelins had a significant effect on his service as a Signals Officer in the Holderness Peninsula. The airborne threat to this strategic region had fundamentally altered the defence arrangements in which he came to play a part until March 1918. The creation of the world’s first air-raid early warning system is explained in detail. The vital part that Post Offices played in this network is presented. His attachment to the Headquarters of the Humber Garrison is shown to have been a return to active service as Officer Commanding a Royal Engineers outpost in the Post Office in Roos. Medical records show this to have been after 1st June 1917. The Zeppelin raids he experienced whilst a patient in the Brooklands Officers’ Hospital are detailed together with the corresponding diary entries of Margaret Strickland-Constable. His duties as a Signals Officer instructor with the 3rd (Reserve) Battalion Lancashire Fusiliers, a training battalion, are illustrated. His attachment to the 9th Battalion Royal Defence Corps during the winter of 1917-1918 was to a unit that needed a battle-experienced Signals Officer to supervise essential, often coded, communication in a focus of the war at the crucial approaches to the Humber Estuary. Finally, the possible reason for the absence of this military detail from the records is suggested.