In his letters to Emilie, Jaan Unt showed himself versatile and valiant, the equal of his two more famous namesakes. As did 100,000 Estonians, he served in the Imperial Russian Army during World War I. He was at perhaps the most important signals centre of the war front, the Warsaw Railway Station Military Police Office from the war's outbreak and in 1915. In 1916, he served as border guard at Tornea, Finland. During Russia's 1917 retreat, he saw action as an infantryman. Throughout Estonia's War of Independence, 1918-20, Jaan Unt was a sapper, a group whose services building and destroying roads, bridges and communications lines were essential to winning the war. Jaan Unt saw action in fierce fighting in southern Estonia and around Pskov (Pihkva) in Russia.