Accounts of American involvement in World War I usually play up the independence of the American Expeditionary Force (AEF) from British or French command on the western front. When the United States entered the war in 1917, President Woodrow Wilson instructed the new commander of the AEF, General John J. Pershing, that because the AEF was to be an instrument of U.S. policy alone, Pershing should not allow American troops to be “amalgamated” into Entente units. From there, stories of American soldiers in the field usually follow Pershing's First Army, assuming that the prohibition on amalgamation was strictly obeyed. In fact, it was not.

Mitchell Yockelson's Borrowed Soldiers shines a light on the usually ignored American divisions that served as part of the British Expeditionary Force (BEF) under Field Marshall Sir Douglas Haig: the Twenty-seventh and Thirtieth National Guard Divisions, organized for their service as the II Corps of the AEF. Yockelson, an archivist at the National Archives and instructor at the U.S. Naval Academy, has combed through unit histories, diaries, and letters from the American, Australian, and British officers who served together as part of Haig's Fourth Army in Flanders. Beginning with the organization of the brand new American army following U.S. entry into the war, Yockelson follows the Twenty-seventh and Thirtieth Divisions through their training in the United States to their arrival on the Continent, interspersing with this tale discussions of tense, high-level negotiations between Pershing and the British and French military officials who pushed the general to let them use all the American troops in their own armies. Both sides eventually compromised, and in mid-August 1918, Pershing allowed the two divisions of II Corps to stay at Ypres with the British forces who had been training them. The Twenty-seventh and Thirtieth worked together with British and Australian divisions to attack and break the Hindenburg Line in late September and carry out the successful Selle River campaign in October.

While dense with interesting detail and anecdotes, the book's early chapters suffer sometimes from their abbreviated length and inconsistent organizing analysis. Too often the reader is left to determine for herself why a chapter's information is significant and how it contributes to a larger point. Happily, Yockelson's analytical focus improves as his story takes the American soldiers into the field in Flanders. He offers colorful and easily followed narratives of the participation of the Twenty-seventh and Thirtieth Division troops in two major operations against the Germans, and he skillfully weighs evidence from a variety of sources on the behavior of the Americans in combat. The troops of the II Corps provided numbers and energy important to their tired allies in the final push to defeat Germany.

Yockelson aims in the book's last chapters to evaluate the contributions of these American divisions that were amalgamated into the BEF. He is explicit about what information his sources do and do not offer, making clear that although we have official American opinions of this partnership (Pershing asked his own officers for assessment reports), we have nothing similar from Haig or his officers and must rely on diaries and letters instead. Yockelson outlines some of the advantages American soldiers under British command enjoyed, compared to their independent AEF comrades, including better supply of food and equipment and better on-the-job training for American staff officers, who could leave the high-command work to the British. And although the author claims that direct comparisons of performance are difficult, the amalgamated Twenty-seventh and Thirtieth Divisions seem to measure up to or even surpass other AEF divisions. Their inexperience led to high initial casualties, but their casualty rates decreased quickly as they learned from the British at the front (220). They also avoided some of the questionable strategies Pershing chose for his independent troops, such as a difficult attack on the Meuse with exhausted and still-green troops (221). Yockelson implies that European training on-site in Europe improved performance, asserting that within the independent AEF, the only three divisions comparable to the British-trained Twenty-seventh and Thirtieth Divisions had been trained in France by French instructors. Discipline, however, was better in the Twenty-seventh and Thirtieth, perhaps because they were the only National Guard units to remain constant in their local composition (the Twenty-seventh Division was entirely from New York; the Thirtieth Division from North Carolina, South Carolina, and Tennessee). Interestingly, this condition seems due to Pershing's neglect of these divisions once they had gone to the BEF: while other National Guard units became mixed when they incorporated replacements, the II Corps never got the replacements it requested, because Pershing considered it unimportant.

Whether Pershing was right to insist on the independence of the untested AEF instead of allowing American units to serve with the experienced British and French armies remains controversial. Yockelson does venture some comparisons between the II Corps and the independent AEF, and he states that Pershing “made the correct decision” to leave the Twentieth and Thirtieth Divisions with the BEF after their training there (223). But the author skirts the larger issue and does not put his comparisons together to make a judgment on the wisdom of amalgamation versus independence. While such careful objectivity acknowledges the complexities of the U.S. position in the war, it also denies readers the educated opinion of one of the few scholars whose research might allow for such a judgment. Even if the United States had maintained an independent army on the western front, might the incorporation of additional separate American units—like those of the II Corps—into British and French armies have helped the war effort?

Although Yockelson declines to wade into the controversy, he has still provided a much-needed illumination of the work of these American soldiers serving with the BEF. As the author makes clear, the mutual respect between these amalgamated troops and their British counterparts would provide a foundation for an even stronger Anglo-American partnership in the next world war.