In the beginning of August 1914, Austro-Hungarian soldiers of
42nd Croatian Home Guard Infantry Division maimed and hanged his father, mother, grandmother, his three sisters, and four of his brothers. His house was also set on fire. Momčilo survived because he was not at home when it happened—his father had sent him to his uncle earlier.
Left without family and without a home, Momčilo went to find the 6th Artillery Division of the
Serbian army, which was near
Gučevo at the time. Major
Stevan Tucović, brother of
Dimitrije Tucović, accepted Gavrić into his unit after hearing about what had happened, and assigned Miloš Mišović, a soldier in the unit, to be Gavrić's caretaker. The same evening, he took revenge by showing his unit the location of the Austro-Hungarian soldiers, and participated in the bombardment, as told by his son Branislav Gavrić in an interview.
At the age of 8, after the
Battle of Cer, he was promoted to the rank of
Corporal by the commander of his unit, and given a military uniform.
When his unit was sent to
Thessaloniki, Major Tucović sent him to
Sorovits where he hastily went through the equivalent of four grades of elementary education.
In
Kajmakčalan,
Field Marshal Mišić was stunned when he saw a uniformed ten-year-old boy in the trenches. Major Tucović explained the situation to him; that Gavrić had been with them since the
Battle of Cer, and that he had both been taught discipline and been wounded during his time in the unit. Mišić promoted Gavrić to
Lance Sergeant, and the order was read out to the whole division
https://en.wikipedia.org/wiki/Momčilo_Gavrić