During the 1920s, the United States Postal Service, and the mail, came under attack from enterprising criminals. In 1921, after several high profile robberies, President Warren G. Harding sent 2,200 Marines to guard mail delivery across the nation. The "Devil Dogs" were assigned to high priority certified mail, items such as cash and negotiable bonds. While the Marines were on guard, not one robbery was attempted. They withdrew in 1922.

By 1926, the postal service was once again a prime target for robberies, which prompted President Coolidge to assign 2,500 Marines to guard duty across the nation. Union Station was one of the biggest economic and transportation hubs in the region.