[2][4] He saw active service in the First World War, which had begun two months before, and served as an acting captain from 14 March to 12 April 1916,[5] and was promoted to the substantive rank of lieutenant on 17 August 1917, back-dated to 1 September 1915.

[6] Promoted to captain on 14 January 1918,[7] he took part in the Kuki Punitive expedition that year and, after the war, was an officer of the North West Persia operations between 1920 and 1921.

A temporary brigadier by this time, he was appointed General Officer Commanding (GOC) 34th Indian Infantry Division on 1 October 1941 with the acting rank of major-general.

Tuker had found a book dated 1879 in a Naples bookshop giving details of the construction of the monastery at Monte Cassino which his division was to attack.

[18] While recovering he assumed light duties as General Officer Commanding, Ceylon from March 1944 to September 1944, before becoming Chairman of the Frontier Commission in India.

[28] Knighted with the KCIE in the 1946 New Year Honours,[29] he was promoted once more to acting lieutenant-general on 21 January and appointed General Officer Commanding-in-Chief, Eastern Command, India.

Tuker, nicknamed "Gertie" when he was in the army, is known for a number of books on military history that he wrote, including The Pattern of War, While Memory Serves and The Yellow Scarf.

[38] In his book Approach to Battle (1963), Tuker commented on his career: "I have tried my hand at many other things in my life - farming, commercial horticulture, authorship, training horses, painting, etching and engraving, and none have I found so testing and so difficult as the planning and conduct of a successful land battle against a worthy foe, whether against the guerrilla or the enemy who is fully equipped for war.