World War IOn April 6, 1917, less than six years after Great Lakes was opened, the U.S. declared war on the Central Powers. By August, the number of trainees grew from 618 to 50,000. Vast tent cities sprang up to house the flood of volunteers. Captain Moffett, Commanding Officer of Great Lakes at the time, organized the huge, influx into "Regiments." Each Regiment of 1,726 men was a self-contained unit incorporating its own administration building, galley, mess halls, dispensary, barracks, and training facilities.
During the war, Great Lakes became the largest training station in the U.S., graduating 126,000 men, over 25% of the U.S. Navy total. During this time, football and the marching band at Great Lakes received national prominence. The 1919 football team won the Rose Bowl led in part by George Halas (later "Papa Bear" of the Chicago Bears) and the renowned marching band conducted by John Philip Sousa, the "March King" performed across the world.
Between the WarsAfter the signing of the Armistice, the United States entered a period of uncertainty followed by an economic recession in 1920 and 1921. A cutback program at Great Lakes began. Most temporary buildings were torn down, rented lands relinquished, and most training was discontinued. In 1933, a spirited local campaign was organized by the Union League Club demanding Congress restore the Station to at least its pre-war status. The petition was successful and a period of minor growth followed. However, in 1922, in the depth of the Great Depression, Great Lakes Naval Training Station closed its doors, being reduced to a maintenance status. Once again, the local community rallied with a vigorous campaign, and on July 1, 1935 the Station was reopened.