The Army in the Interwar: Training a Professional Army in a Turbulent Era

Immediately following the Armistice in November 1918, the U.S. Army experienced its first significant victory on the world stage. Yet despite the peace declared in Europe, thousands of American soldiers remained deployed in far-flung and challenging environments. In northern Russia, for example, soldiers found themselves fighting in the bitter cold of the Arctic tundra. They were part of the Allied intervention in the Russian Civil War—a mission that had been launched by President Woodrow Wilson. Approximately 8,000 troops, under the command of Maj. Gen. William S. Graves, landed at Vladivostok to secure essential war materiel, keep a key segment of the Trans-Siberian Railway open, and support the stranded Czechoslovak Legion. Meanwhile, a smaller expedition known as the “Polar Bear Expedition” of about 5,500 men, deployed to Arkhangelsk, operated under British control. Despite the severe conditions—sub-zero temperatures, dense wilderness, and constant skirmishes—the Americans pressed on, only leaving the region in April 1920 after enduring roughly 400 casualties.

Back in the United States, the battlefield success overseas contrasted sharply with the political and military landscape at home. Between 1919 and 1922, Congress demobilized the Regular Army sharply, reducing its numbers from nearly three million to just over 130,000, with only 200,000 National Guardsmen retained for federal service. This rapid downsizing, allied with the murky outcomes in Russia, sparked a debate over the future character of America’s military. Many wondered how to maintain a ready, professional force in an era of shrinking budgets, persistent isolationist sentiments, and an uncertain international order.

At the same time, the interwar period spurred significant technological innovation. The innovations of World War I, such as tanks and aircraft, had set the stage for modern warfare. In the United States, however, the production and training related to these new technologies met with substantial challenges. For instance, an order was placed for over 1,000 International Tanks (the Mark VIII Liberty Tanks), yet the end of the war meant that none were completed as originally planned. Instead, between 1919 and 1920, only 100 tanks were produced at Rock Island Arsenal—with each costing around $35,000 at the time. Chronic budget cuts forced many units to train with improvised equipment: jeeps or combat vehicles were re-christened as “tanks” and cardboard cutouts sometimes simulated machine gun turrets. Similarly, the Army Air Corps found itself grappling with technical limitations. Debates about the role of aviation in military strategy led to only modest investments in new aircraft throughout the 1930s, limiting the number of active pilots and the overall effectiveness of air power.

In response to these multifaceted challenges, military planners began to formulate comprehensive peacetime mobilization strategies. The 1923 General Staff plan envisioned six field armies, each comprising roughly 400,000 soldiers and capable of mobilizing over one million troops within four months if needed. The United States was divided into geographic zones, with each field army assigned to a specific region. In 1931, General Douglas MacArthur’s approval of a Field Army Headquarters marked another critical step toward rapid mobilization. Despite these preparations, budget constraints and the harsh realities of the Great Depression complicated the task of training and equipping soldiers. In 1935, the First Army conducted training exercises involving approximately 35,000 personnel, yet limited materiel and the use of surrogate equipment resulted in simulations that were far from ideal. These exercises were even observed by foreign military delegations from nations like Japan and Germany, who were keeping a keen eye on America’s military preparedness.

The interwar period also saw the development of the famed Rainbow Plans—a series of contingency war strategies designed to address potential conflicts with a range of global adversaries. Each plan was tailored to specific regions: War Plan Black focused on Germany; War Plan Grey and Violet on Central America and the Caribbean; War Plan Brown on the Philippines; War Plan Tan on Cuba; and War Plans Red, Yellow, Gold, Green, Indigo, Purple, Blue, and White covered a broad spectrum from Britain and China to domestic defense and internal unrest. In particular, War Plan Orange was devised for Japan—and served as the blueprint for U.S. operations in the Pacific Theater.

By the eve of World War II, it was clear that the United States faced a dilemma. While the rapid mobilization of its industrial base had been demonstrated in World War I, the process of fielding equipment overseas had been sluggish. Under the strain of economic depression and persistent resource shortages, American military planners recognized that maintaining and training a professional army was a complex balancing act. Leaders like Lieutenant General Hugh Drum, and later LTG Lesley J. McNair, underscored the urgency of continuous training and the development of robust mobilization plans. Soon after Germany invaded Poland and France fell, the nation’s first peacetime draft was launched, mobilizing around 900,000 men and signaling that, despite its rocky start, the U.S. military was committed to rising to the challenges of a new era of warfare.

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