After graduating, Shallash was made a "yüzbaşı" (captain) in the Ottoman Army; this was a high rank for a new graduate and its attainment was due to the imperial favor shown to the sons of rural sheikhs in the military. In 1911, he was sent to fight in Libya against the Italian invasion. There, he encountered the prominent Ottoman officers Aziz Ali al-Misri, Mustafa Kemal and Enver Pasha. After the Ottoman defeat in Libya, Shallash was reassigned to the Balkan front, where he commanded a unit of soldiers from Palestine. Sources are not clear about Shallash's service with the Ottomans during World War I.