On the outbreak of war Capt Kaye joined the Red Cross and with his friend, Lt Maurice Mackenzie, RAMC, organised a hospital at Chateau Laversine, which was a place at the disposal of the British Red Cross Society by Baron Robert De Rothschild. A large number of French and British wounded were treated there until the advance to the Aisne caused the hospital to be evacuated. Kaye and Mackenzie then returned home and joined the RAMC. They were posted to the 43rd Field Ambulance, and after training at Aldershot went with the ambulance to France in April.