While Lotman was in his second year of university, he was called to serve in the military. During the Second World War he served as a signal operator in the artillery regiment. He was awarded three military orders and four medals.
During the war, he actively engaged in self-education: he studied French, read textbooks, articles and monographs on philosophy, the history of literature and Russian history and was interested in the era of Ivan Grozny. In letters to his sister, Lidia, in 1943, he had already begun to write statements about the need to look at culture as a whole, distinguishing between synchronic and diachronic levels.