After relinquishing his position as DCIGS to General Sir Philip Chetwode in 1920, Harington assumed command of the Army of the Black Sea, occupying parts of Turkey and later used to enforce a neutral zone established by the nominal signing of the Treaty of Sèvres during the Greco-Turkish War. Succeeding General Milne, Harington had under his command the British 28th Division at Istanbul, a Greek division at İzmit and a Greek regiment at Beykoz. Additional contingents supplied by the French and Italian armies, under General Charpy and General Mombelli respectively, were subordinated to Harington when he became C-in-C, Allied Occupation Forces in Turkey. In 1921, the Greek Army in Anatolia initiated an offensive against Mustafa Kemal's forces and maintained their advance with the intent of capturing Angora. Some 50,000 Greeks were redeployed to Eastern Thrace, threatening Istanbul. Harington later recalled in his memoir that during a social event, Turkish officials offered some 20,000 of its soldiers to defend the city, less than a year before the Chanak Crisis that prompted Greece to offer the assistance of 20,000 of its troops.