With the Korean War occurring, Mizell had been drafted to serve in the United States Army as early as 1952, but he managed to get his service deferred twice because he was the support for his mother and grandmother. Finally, shortly after the 1953 season ended, he reported to Fort McPherson, Georgia, where he would be stationed for the next two years. Mizell, who walked with a "two-furrow" stride, had to make a special effort not to step on the heels of the soldier in front of him when he was marching in ranks. He saw no combat, instead winning 36 games (with only two losses) for the fort's baseball team. Mizell threw four no-hitters and 16 shutouts, helping the team reach the Army baseball championship tournament at Fort Belvoir, Virginia, in 1955. A sergeant by the time he was discharged, Mizell had struck out 324 batters in two years of service.