He became a professional (soldier) officer in 1928 in the "Zaniemieńskich" ("Beyond Niemen River") 4th Regiment of Uhlans in Vilnius garrison.

In the first days of September, the 13th Regiment of Wilno Uhlans "Wileńskich" fought near Piotrkow; next, it crossed the Vistula near Maciejowice.

The charge has become a symbol of the closing of the chapter in the history of the Polish military: the end of the last Islamic/Tatar unit.

Soon after, 13th Regiment of Wilno Uhlans was dispersed by the enemy during fighting near the village of Suchowola near Lublin.

Jeljaszewicz together with the few of his men who have not been dispersed tried to reach the Romanian Bridgehead, but was stopped, and spent the rest of the war in a German oflag.