He enlisted in the U.S. Navy on November 5, 1940. He received navy recruit training at Naval Training Station, Norfolk, Virginia and hospital corpsman training at the Norfolk Naval Hospital, Portsmouth, Virginia. In March 1941, Willis was promoted to seaman second class and was briefly assigned to the Naval Hospital, Parris Island, South Carolina, transferring to Naval Air Station, Jacksonville, Florida, in the late spring.
He enlisted in the U.S. Navy on November 5, 1940. He underwent navy recruit training at Naval Training Station, Norfolk, Virginia and hospital corpsman training at the Norfolk Naval Hospital, Portsmouth, Virginia. In March 1941, Willis was promoted to seaman second class and was temporarily assigned to the Naval Hospital, Parris Island, South Carolina, before being reassigned to Naval Air Station, Jacksonville, Florida, in the late spring.