Plummer defended the 88th Aero Squadron's aerial reconnaissance mission to photograph the Vesle River sector of France during World War I.

[2] He briefly worked for Northwestern Mutual Life Insurance Company before enlisting with Battery A of the 101st Field Artillery Regiment in Massachusetts of the American Expeditionary Forces.

[3] These actions helped Plummer's squadron capture 30 critical photographs of German enforcements[4] and earned him the Distinguished Service Cross, the American military's second highest honor.

[5] General John J. Pershing awarded Plummer the medal in the name of President Woodrow Wilson in October 1918.

"[11] After Plummer's death, James F. Clark, a former 101st captain, gave a cup in his honor to Boston's Indoor Polo League.