Christy Mathewson, one of the greatest pitchers of all time, retired during the 1916 season at the age of 35.

He joined the war effort in 1918, serving in France as captain in the newly formed Chemical Warfare Service. - National Baseball Hall of Fame

Mathewson and Ty Cobb were never teammates, but they did serve together in the United States Army in France during World War I.

They were both also part of the first National Baseball Hall of Fame induction class in 1936.

- National Baseball Hall of Fame

This 1917 Ty Cobb model bat was used in games played by United States servicemen overseas during World War I. - National Baseball Hall of Fame

This medal was won by U.S. Army soldier and Major Leaguer William E. Marriott from Pratt, Kan., while playing American Expeditionary Forces baseball in Le Mans, France.

- National Baseball Hall of Fame

Marriott won another medal while playing American Expeditionary Forces baseball in Le Mans, France. - National Baseball Hall of Fame

Eddie Grant played 10 Major League seasons (1905-15) with the Cleveland Naps, Philadelphia Phillies, Cincinnati Reds and New York Giants.

Grant, who retired after the 1915 season, enlisted in the Army immediately after the United States entered World War I. Not long after his enlistment, Captain Grant was sent to the front lines in France. - National Baseball Hall of Fame

On Oct. 5, 1918, Grant and his men marched to the valley where the famed "Lost Battalion" was stranded before German shelling stopped the advance. Grant was killed in the ensuing battle.

The New York Giants held a memorial service for their former player in 1919.

- National Baseball Hall of Fame

Grant was the only Major League player to die serving in World War I. His alma mater, Dean Academy, produced a eulogy book as a tribute. - National Baseball Hall of Fame

In 1929, the Giants dedicated a plaque honoring Grant that stood in front of the 483' mark in center field at the Polo Grounds. The plaque disappeared after the Giants' last game at the Polo Grounds in 1957. - National Baseball Hall of Fame

The fact that the Grant plaque didn't make the trip west to San Francisco gave rise to a supposed curse of the Giants.

To reverse the curse, the San Francisco Giants unveiled a replica plaque on Memorial Day 2006. Four years later they became world champions for the first time since leaving New York.

- National Baseball Hall of Fame

This baseball was used in 1917 by sailors on the island of Guam and later presented to Guam's United States Naval Governor Roy C. Smith. - National Baseball Hall of Fame

Catcher Hank Gowdy of the Boston Braves was the first active Major League player to enlist in World War I. He saw action in France, serving with the 166th Infantry Regiment.

- National Baseball Hall of Fame

Gowdy returned to the big leagues after his service in World War I, playing until 1930 when he was 40 years old. He re-enlisted during World War II at 53 and served as Chief Athletic Officer at Fort Benning. - National Baseball Hall of Fame

Members of the 1917 Cleveland Indians taking part in military drills during Spring Training.

- National Baseball Hall of Fame

This headline from the New York Times from Aug. 3, 1918, announces the end of the baseball season. The 1918 World Series was played early, making it the first Fall Classic not played in October. - National Baseball Hall of Fame