Harmon served in the Navy during World War II spending all 3 years stateside at the Great Lakes Naval Training Station, playing baseball.

[2][3] Harmon and longtime teammate and friend Art Grove then reunited with Friddle to play for the University of Toledo, where they helped an all-freshman squad (that included Gary, Indiana's Davage Minor) advance to the championship game of the National Invitation Tournament (NIT), losing to St. John's.

[5][6] During the summer of 1947, Harmon briefly played professional baseball with the Negro league Indianapolis Clowns, using the alias "Charlie Fine" to preserve his collegiate eligibility.

Pinch-hitting for pitcher Corky Valentine against Lew Burdette, Harmon flied out in the seventh inning of a 5–1 loss to the Milwaukee Braves at County Stadium.

[8] In that game he came to bat after another rookie, Nino Escalera, an Afro-Latin American from Puerto Rico who pinch hit immediately before Harmon to become the first black player to appear for the Cincinnati franchise.

Starting and leading off for the Reds at home in Crosley Field in a 3–2 win over the Chicago Cubs, Harmon singled in the first inning off Howie Pollet.

[13] In addition, in cooperation with the Cincinnati Reds, a renovated ball field was named in his honor in the multi-use municipal Volunteer Park.