He played for one season for the Calgary Currie Army before being discharged as medically unfit to serve.
After returning in 1944–45, he signed a free agent contract with the Toronto Maple Leafs.
The Leafs beat the Detroit Red Wings in seven games and McCool set a franchise record for most shutouts in the postseason.
This stood until the 2011 Stanley Cup Finals, when it was beaten by Boston Bruins netminder Tim Thomas, who only gave up eight.
Frank McCool has an arena named after him in the southeast community of Lake Bonavista in the city where he was born, Calgary, Alberta.