Soon after Otto Carius graduated from school, World War II broke out. Carius enlisted in the army and was only accepted after twice being rejected as unfit for military service due to being underweight. He first served in the infantry before volunteering for the Panzer branch; his father referred to tanks as "metal deathtraps."[1][1][2] In 1943, Carius was transferred to the 502nd Heavy Panzer Battalion and fought in the northern sectors of the Eastern Front.