After the 1942 season, Lavelli was drafted by the U.S. Army as American involvement in World War II intensified. After basic training and a number of other specialized courses on land-sea assaults, he was sent with the 28th Infantry Division to fight in the European Theatre of World War II. There his division landed on Omaha Beach, part of the Allied invasion of Germany-occupied France in 1944. He was involved with American forces in Germany's Battle of the Bulge offensive and in the Siege of Bastogne later the same year. One in five members of his division was killed in battle.