In 1914 Yitzhak Ben-Zvi and David Ben-Gurion, the president and prime minister of Israel after 1948 respectively, were in the Ottoman capital studying law at Istanbul University.  They had studied Ottoman Turkish and embarked on their legal studies in the hope of one day serving in the Assembly of Deputies as elected representatives from Jerusalem.  With war on the horizon, they made their way back to Palestine, where they volunteered for military service in the Ottoman army.  They also proposed the formation of a Jewish legion to fight under the Ottoman banner, but their intiative fell on deaf ears…We have no way of knowing how things might have turned out had Ben-Zvi and Ben-Gurion been allowed to suit up in Ottoman uniform…

Moshe Sharett, another future prime minister of Israel and said to have been fluent in both Arabic and Turkish, served in the Ottoman army during the Balkan Wars and all through the First World War, even beyond the announcement of the Balfour Declaration and the British occupation of Jerusalem in December 1917.

That is all from the quite good The War That Made the Middle East: World War I and the End of the Ottoman Empire, by Mustafa Aksakal.