E. Brooke Lee's great-uncle was Montgomery Blair, who served as postmaster general during Abraham Lincoln's presidency.

Lee and Frank L. Hewitt, another businessman and real estate investor, helped build an armory and organize a new Maryland Guard company, Company K, located in Silver Spring in 1914; the armory was later remodeled and now houses the Silver Spring Volunteer Fire Department.

Lee commanded Company K and helped General John J. Pershing pursue Mexican revolutionary and bandit Pancho Villa,[5] who had been running border patrols along the Rio Grande River into New Mexico.

The National Guard unit of 150 men was sent to Camp McClellan, near Anniston, Alabama, in August 1917 for a period of ten months of training, emerging as Company K of the 115th Infantry, 29th Division of the American Expeditionary Force.

While commanding of a raiding party against the Central Powers near Balschwiller, France, on the morning of August 31, 1918, Lee led soldiers' advance through the enemy wire.

[6] Lee was the last person to leave the opposing forces' trenches, and he carried wounded soldiers back through the counter-barrage.

[6] Lee spent the entire day of August 31 in a shell hole in no man's land because he wanted to help all wounded soldiers return to the American line.

In June 1918, Lee was discharged from active duty with the rank of lieutenant colonel, and he was generally considered a war hero.

[citation needed] In 1916, Lee helped establish the Washington Suburban Sanitary Commission to control the development of regional water and sewer systems that were necessary for the county's growth.

[8] In the early 1920s, Lee began to purchase large tracts of farming land and founded the North Washington Realty Company to develop those properties as racially restricted suburban communities.

[10] These restrictive covenants forbid the purchase or reselling of these properties by people of "African descent" and remained in effect until 1948 when the Supreme Court in Shelley v. Kraemer ruled they were unenforceable.

[citation needed] In January 1927, Lee proposed the creation of the Maryland-National Capital Park and Planning Commission, led by three commissioners appointed by the governor.