In 1913 and the early part of 1914, following short spells at the War Office, he carried out a survey across the Sinai Peninsula to Beersheba, under the auspices of the Palestine Exploration Fund.
The Negev Desert was of strategic importance, as it would have to be crossed by any Ottoman army attacking Egypt in the event of war and the survey updated mapping of the area, showing features of military relevance such as water sources.
[2] At the end of 1916, after a spell in France, he was appointed Chief of the British Military Mission with the Sharif of Mecca's forces in the Hejaz where he again worked with Lawrence and played a key role in the Arab Revolt.
Lawrence was later to pay Newcombe a blended compliment in his book Seven Pillars of Wisdom when he wrote; 'Newcombe is like fire,' they (the Arabs) used to complain, 'he burns friend and enemy', referring to his enthusiasm for destroying this vital artery that supplied the besieged Ottoman garrison in Medina.
[3] Newcombe was captured during the Third Battle of Gaza leading a party of seventy men of the Imperial Camel Corps behind enemy lines to cut the Hebron road with machine-gun fire to prevent the Turkish garrison of Beersheba escaping the British advance.
Lowell Thomas, in his book With Lawrence in Arabia (1924), wrote "But months later, after having survived smallpox and all the other luxuries of Turkish prison life, the colonel escaped from his cell in Constantinople through the aid of a beautiful Syrian girl, who then concealed him in her home."
"Then, as any born hero of melodrama would expect to do as the climax to his romantic career, he married the beautiful Syrian girl who had helped him escape---and we hope lived happily ever after."
As noted in the memoirs of David Ben-Gurion, Israel's first Prime Minister, Newcombe was in December 1937 involved in an effort to start negotiations between the Zionist Movement and prominent Palestinian Arabs, aimed at trying to end the violent confrontations then engulfing Mandatory Palestine.