General Cayley was an old Cliftonian, and was gazetted to the Regiment from the Royal Military College in March, 1890. After a brief stay with the 2nd Battalion, then stationed at Limerick, he was posted to the 1st Battalion in India and joined them with a draft that same year. He served with them at Poona, Kamptee, Rangoon and Aden until 1896, when he came home with the Battalion to Tregantle Fort, Devonport. He was promoted Captain in June, 1899, and served with the 1st Battalion throughout the South African War and afterwards at Templemore.
In July, 1904, he was promoted Major and in that rank he was posted to the 2nd Battalion in Ceylon in 1905, serving with them at that station, Ahmednagar and Jhansi. As Second-in-Command he came home with the Battalion to Aldershot in 1913. In 1914 he was promoted Lieut.-Colonel and proceeded to Burma to take command of the 4th Battalion.
Then came the First Great War 1914-18. He mobilized and commanded the 4th Battalion which formed part of the 88th Infantry Brigade, 29th Division. He commanded the Battalion at the historic landing at Helles in Gallipoli, and through various actions on the Peninsula in which the 4th Battalion fought with such distinction.
In 1915 he was appointed Brigadier-General and assumed Command of the 88th Infantry Brigade, taking an active part in both the Suvla and Helles evacuations which were so successfully carried out. The 29th Division, after a re-fit in Egypt, was moved to the Western Front.
General Cayley commanded the 88th Infantry Brigade at the opening Battle of the Somme in July, 1916, and during subsequent operations until at the Battle of Monchy-le-Preux in April, 1917, where his Brigade was heavily engaged. At this action General Cayley was gassed. On recovery he re-assumed command of the Brigade and commanded it until the Battle of Ypres, 1917 (Passchendaele), when once more he was severely gassed with the whole of his Brigade Staff.
Lieut.-Col. D. E. Cayley