On Jun 14th 1914. he married Tinka – Hristina Topuzovic and went for honeymoon to Dalj, where he heard about the beginning of the WWI.
All citizens of Serbia present at the Austro-Hungarian territory at the time had been rounded up and imprisoned at the war camp in Osijek and later moved to Karlovac. Aided by friends and helped by state official from Zagreb Milankovic was allowed to live in Karlovac. But on October 21st he had to go to Nezider with all other Serbian citizens. His wife went to Vienna to talk to professor of High technical School in Vienna Emanuel Czuber, who was his mentor and a good friend.
Professor Czuber had achieved, through his social connections, that Milankovic was released from prison and given a permission to spend his captivity in Budapest with all civil rights granted including the right to work. His was only restricted not to leave town and to report to police office once a week. He also received a notice for the head of library of Hungary academy of science, a mathematician who allowed him to use the library even after the closing time. He used it to study all the aspects of insolation of the Earth and the distribution of Sun’s radiation at the Earth surface by means of contemporary literature that was available and he also wrote several papers
and a monograph based on his previous research on the subject. This monograph was later translated by his friend, professor Ivan Djaja, and published in France in 1920.
After his return to Belgrade he was elected professor in ordinaries.
He was a consultant for planning and implementation of construction projects of hangars and workshops at airfields at Bezanija, Zagreb, Skoplje, Kraljevo and Pancevo, air force command headquarters at Zemun, tobacco factory at Nis, The Institute for manufacturing banknotes and coins etc.
He designed his own home at Profesorska kolonija.