During World War I, he was conscripted into the Imperial Russian Army in January 1915 and assigned as a ryadovoy to the 195th Reserve Battalion of the Moscow Military District.

Wounded in battle on 4 July 1915 near Kholm, Yershakov returned to his regiment after treatment, and graduated from its training detachment as a squad leader.

In November 1916 he was transferred to the 525th Infantry Regiment, with which he fought in battles on the Northern Front in the regions of Vilno, Krevo, and Smorgon.

[1] Yershakov immediately joined the Red Army in April 1918 during the Russian Civil War, serving as a rifleman guarding the Vasileostrovsky District Soviet in Petrograd.

From December 1932 to November 1934 he received advanced training at the special department of the Frunze Military Academy, then was appointed commander of the 29th Rifle Division.

[1] The 22nd Army was ordered to board trains bound for the Western Dvina line on 13 June, becoming part of the Reserve of the Supreme High Command.

In October, during Operation Typhoon, German troops broke through Soviet defenses and encircled several armies, including the 20th, in the Vyazma pocket.

[1] After the destruction of his 20th Army, Yershakov found himself and a part of the commanders and commissars of his headquarters attempting to break out of encirclement for the second time in the past two months.

Moving to the east, by 2 November, the group reached the station of Machino, 28 kilometers west of Sukhinichi, where they decided to rest for the night in one of the houses.

The prisoners of war were sent to the General Walter von Unruh, railway construction commander of Army Group Center on 4 November.