According to The Middlesex County Times of 8 January 1916, Sydney had enlisted for the army under the Derby scheme. He went into the York and Lancaster regiment, being an infantry regiment. His brothers Edgar and Arthur also joined the same regiment but it not known if they all joined up together. It is a point of interest to note that a gentleman called John Robert Folker who lived at Windsor also served in this regiment and died of ounds in Italy in 1918. They were not directly related and one wonders how they both came to be in a regiment from outside their area. Was it perhaps that had been a recruiting drive in the area ?

Sydney spent some time at Clipstone camp in Nottinghamshire during which time Vera and Doady stayed in the village. He was also possibly stationed at Bulford camp for a while. He was despatched to France but was recalled, without getting off the boat, to train others in musketry. He also trained horse gun carriage crews on land belonging to Twyford Abbey which was close to his home in Brentham. He had reached the rank of sergeant when invalided out of the army due to his weak chest. After demobilisation, Sydney received a temporary allowance until back in work.

A few mementos of Sydney's WW1 army uniform remain in the possession of his descendants, also the military form of the registration of his birth.

During the second World War, Sydney served in the Home Guard at Marlow Bottom and a folder of papers relating to his service have survived and been donated to Marlow Museum.