Having first seen combat in World War II in July 1941 during the initial phase of Operation Barbarossa, Boyko was the deputy commander of a reconnaissance battalion at the time. In August he became the commander of the 83rd Tank Battalion, but he was soon chosen for transfer and made the commander of a battalion in the 32nd Tank Brigade. He went on the participate in the Battle of Moscow and the fighting for Tula, and on 28 November he was wounded. Once he recovered in February 1942, he served as a deputy battalion commander in the 1st Tank Army under the command of
Mikhail Katukov. In April he took command of his battalion. In September he was placed in command of the 17th Tank Regiment and participated in
Battle of Rzhev. His regiment was honored with the Guards designation and renamed the 69th Guards Tank Regiment for its actions in combat during the summer of 1943. The unit went to fight in the defense of Kursk and in the
Belgorod-Kharkov Offensive. He was badly wounded during the battle. On 28 December 1943, the 69th Guards Tank Regiment expelled German forced from Koziatyn as part of the
Zhitomir–Berdichev Offensive. Upon receiving orders to advance to Koziatyn, Boyko and his unit began a 35-kilometer march towards the city. The Germans fled in panic at the surprise advance, despite being numerically superior. The attack resulted in the destruction of 20 enemy tanks, one armored train, two vehicles, and two artillery batteries were destroyed. In addition, over a thousand German soldiers were killed and 150 captured. After the offensive, German forces launched a two-day counterattack. Boyko and his unit managed to hold the city despite heavy enemy fire while waiting for reinforcements. For his success in Koziatyn, he was awarded the title Hero of the Soviet Union on 10 January 1944. Less than a month later he was placed in command of the 64th Guards Tank Brigade, which would soon have success during the Proskurov-Chernivtsi operation. In March 1944 Boyko's brigade crossed the Dniester River, advanced 70 meters, and crossed the Prut river, and then advanced into the city of Chernivtsi. Because the brigade had advanced so quickly, they approached the city without many reinforcements and had to fight hard until the remainder of the 8th Guards Motorized Corps arrived before they could completely expel German forces from Chernivtsi. After the successful offensive in the city the 64th Brigade began to head towards Romania. On 26 April 1944 Boyko was awarded the title Hero of the Soviet Union a second time for his leadership of the brigade. He then went on to participate in the
Lvov-Sandomierz and
Berlin offensives. ==Postwar==