The 42nd Division, or “Rainbow Division” as it was known popularly, was composed entirely of unproven National Guard units hailing from twenty-six different states and the District of Columbia. For that reason, there were many who thought the division would never see combat when it deployed to France in October 1917. However, the division would spend 164 days in combat during World War I, a number exceeded by only two other American divisions. Despite the doubts of General John J. Pershing and many senior American officers regarding their ability to serve in combat, the division would come to be viewed by the Allies and their German opponents as one of the best combat divisions in the American Expeditionary Forces. As a result, the Rainbow Division was chosen to lead the American offensive in the Saint Mihiel salient, the first offensive planned and led by the American army in World War I. The division went on to play a critical role in the final offensive of the war in the Meuse-Argonne, where these battle-hardened National Guardsmen were the first Allied unit to finally break through the main German lines of resistance, the heavily fortified Kriemhilde Stellung, which had stopped assaults by three other American divisions.
Approach to Final Victory: America's Rainbow Division in the Saint Mihiel and Meuse-Argonne Offensives by historian Robert Thompson, chronicles the efforts of the Rainbow Division during these final two Allied offensives that were key to the ultimate Allied victory. Based on letters, journals, action reports, and unit histories, the challenges, set-backs, and accomplishments of the division stand as a fitting symbol of American valor and sacrifice during the “war to end all wars.”

American forces entered World War I combat in October 1917, but it was not until July 1918 that they went on the offensive for the first time. Among the units selected for this operation was the 42nd Division, or the “Rainbow Division” as it was known popularly. This division, which was composed of National Guard units from twenty-six states, including Joyce Kilmer’s 69th New York Infantry, would spend 164 days in combat, a number exceeded by only two other American divisions. However, it was the nine days from July 25 to August 2, 1918 that were the most terrible and heroic in the division’s history. General of the Army Douglas MacArthur, who served as the division’s chief of staff, later said of the Rainbow Division’s fighting during those pivotal days, “There was neither rest nor mercy.” During those nine days, the Rainbow Division would spearhead the Allied attack in the Aisne-Marne region, the final phase of the Second Battle of the Marne, which saw the last major German offensive on the Western Front defeated. Unfortunately, American leadership proved to be completely unprepared for a dynamic war of maneuver. Basing decisions on wildly inaccurate information about the Germans, senior commanders ordered the men of the Rainbow Division to make ill-advised assaults again and again with little support. Facing an enemy who was determined to hold itspositions, these National Guardsmen fought with courage and determination to gain what was often only yards of ground, and did so at a deadly cost. 

In Nine Desperate Days: America’s Rainbow Division in the Aisne-Marne Offensive, historian Robert Thompson chronicles the hardships and tenacity of the men from the 42nd Division during this pivotal campaign. The Americans did not break despite heavy losses, and were able to drive the Germans back from territory they initially gained. The efforts of the Rainbow Division during Aisne-Marne were key to the ultimate Allied victory and are a symbol of American valor and sacrifice during the “war to end all wars.”

Finalist for the 2021 Army Historical Foundation Distinguished Writing Awards in Unit Histories
Americans Face the Horror of a Modern European War for the First Time  
When America entered World War I in April 1917, state National Guard units had never planned to mobilize for this kind of war, and the men who made up the hometown companies of each regiment never imagined that they would be asked to fight in what was then the most savage war in human history—they were “innocents” being thrown into a horrendous European conflagration. Made up of companies from ten Ohio towns, the 166th Infantry Regiment became part of the famous 42nd Division, known as the “Rainbow Division.” They were the third American division to arrive in France, where they fought courageously in the trenches at Lunéville and Baccarat before being a key part of the American effort in the Second Battle of the Marne and the Saint Mihiel and Meuse-Argonne offensives. Despite their initial lack of training in modern warfare and weapons, the 166th Infantry compiled an impressive combat record. However, that record came at a terrible cost, with the regiment suffering over two thousand casualties in just nine months of fighting. While they battled the Germans, these hometown Guardsmen lived in trenches and foxholes for weeks at a time, while subsisting on canned beef and coffee amid near constant rain, deep mud, rats, and body lice that made their lives miserable. Because of poor planning and leadership from higher headquarters, they were often asked to achieve impossible objectives amid withering enemy machine-gun fire without proper logistics or artillery support. Yet, despite these challenges, they would persevere, overcome, and emerge victorious.
    Using regimental histories and the letters and diaries of the soldiers who fought in France, Suddenly Soldiers: The 166th Infantry Regiment in World War I by author and historian Robert Thompson tells the compelling story of the young men—“citizen soldiers”—who have always borne the cost of America’s freedom with quiet courage.