Волховский фронт
Petrzhak served in the military intelligence company of a CIWS regiment first as a junior lieutenant, and later as a senior lieutenant. On 28 June 1941, he participated in the battle of Karelian Isthmus. Later, he fought in Volkhov Front. In March 1942 he was ordered to leave the army and join evacuated Radium Institute scientists in Kazan.