March 6 1915, Athens—In the Dardanelles campaign so far, Greece, though officially neutral, had lent indirect support by letting the Allies use her nearby Aegean islands for staging. As planning moved towards a land invasion, the Greek role became more contentious. Greek Prime Minister Venizelos had offered the use of a full corps in the invasions. However, the Russians, thinking about the post-war division of Turkey, was staunchly opposed to Greek involvement—the Russians wanted control of the straits, and the threat that the Greeks would try to take historically Greek Constantinople was too great. As a result, they told the British on the 3rd that “The Russian Government could not consent to Greece participating in operations in the Dardanelles, as it would be sure to lead to complications.” Frantic diplomacy followed, including trying to bring the Russians around or trying to bring the Greeks fully into the war (including aiding their regional rival, Serbia). On the 6th, Churchill wrote (but did not send) a letter to Foreign Minister Grey ending with “If you don’t back up this Greece—the Greece of Venizelos—you will have another which will cleave to Germany.”

However, all of this was moot on the 6th, as Greece’s King, who was married to a German, refused to allow Greek troops to be used in the Dardanelles, forcing Venizelos to resign.

Sources include: Randal Gray, Chronicle of the First World War (Volume I); Winston Churchill, The World Crisis (Volume II).