Answer by taking a quote from the following article:

William Miller Edwards (June 21, 1905 - June 12, 1987) was an American football player and coach. He served as the head football coach at Western Reserve University, Vanderbilt University and Wittenberg University in a career lasting more than 30 years, compiling a win-loss-tie record of 168-45-8. Edwards also coached the Detroit Lions of the National Football League (NFL) from 1941 to 1942, tallying a 4-9-1 record, and served as an assistant coach for the NFL's Cleveland Browns in the late 1940s. Raised near Massillon, Ohio, Edwards was the son of an immigrant from Wales who worked in the area's coal mines.

Having built a strong record at Western Reserve, Edwards was in the running for head coaching roles at a number of larger universities and professional teams. He met with officials at Marquette University and was considered a candidate for coaching duties at Colorado University and for the National Football League's Detroit Lions. After visiting with Lions owner Fred Mandel, Edwards ultimately was hired in February 1941 to succeed George Clark. Both Edwards and Dugan Miller signed two-year contracts. Edwards was given a $10,000 annual salary ($166,380 in 2017 dollars), more than double the $4,420 he was paid at Western Reserve.  Edwards's stint as the Lions coach was unsuccessful. He guided the team to a 4-6-1 record in 1941, and Mandel fired him after three straight losses to begin the 1942 season as the team's roster was depleted by players' service in World War II. Detroit went on to lose all the rest of its games after John Karcis was named his replacement.  Edwards enlisted in the U.S. Navy later in 1942 as America's involvement in the war intensified. While in the military, he served at St. Mary's Pre-Flight, a training program in California, and coached the Air Devils football team there. He also served at a base in Pensacola, Florida. Edwards was discharged in 1946, and spent a year in the sporting goods business in Cleveland, Ohio before reuniting with Brown, who had become the first coach of the Cleveland Browns in the All-America Football Conference (AAFC). Edwards took a position as a tackle coach and remained with the team for two seasons. He coached tackles including Ernie Blandin, Lou Rymkus and future Pro Football Hall of Fame member Lou Groza. The Browns won the AAFC championship in both of Edwards's years as an assistant; the team won all of its games in 1948, turning in professional football's first perfect season.

What branch of military did he serve in?
Having built a strong record at Western Reserve,