James Guthrie Harbord (March 21, 1866 – August 20, 1947) was a senior officer of the United States Army and president and chairman of the board of RCA. During World War I, he served from mid-1917 to mid-1918 as chief of staff of the American Expeditionary Forces (AEF), commanded by General John J. Pershing, before commanding a brigade and briefly a division and then the AEF Services of Supply. In the former role he was, in the words of former soldier-turned historian David T. Zabecki,

The U.S. Army's first modern operational-level chief of staff in a combat theater, and he would be the model for all others who followed. He played a key role in developing the staff structure and organization used throughout the U.S. military to this day, as well as by most NATO countries. He was one of the most influential U.S. Army officers of the early 20th century.

Harbord was born on March 21, 1866, in Bloomington, Illinois, the son of George W. and Effie (Gault) Harbord. His family moved when he was four, and Harbord was raised in Pettis County, Missouri and Lyon County, Kansas. He graduated from Kansas State Agricultural College, later renamed Kansas State University, with a Bachelor of Science degree in 1886. After unsuccessfully applying to the United States Military Academy (USMA) at West Point, New York, Harbord taught school, and afterwards taught at the agricultural college. In January 1889, Harbord enlisted in the United States Army, joining the 4th Infantry Regiment as a private. He served in the enlisted ranks at Fort Spokane, Washington and Fort Sherman, Idaho until July 31, 1891, and advanced to corporal, sergeant, and regimental quartermaster sergeant. In August 1891, Harbord applied for a commission and was one of several non-commissioned officers selected to take a competitive examination. He finished first of the 12 successful candidates and received appointment as a second lieutenant in the 5th Cavalry Regiment, with which he served first at Fort Reno, Oklahoma, and later at Fort Leavenworth, Kansas. He received a Master of Science degree from Kansas State Agricultural College in 1895.

Harbord's first overseas experience came as a member of the occupation army in Cuba after the Spanish–American War. On January 21, 1899, during an extended leave, he married Emma Yeatman Overshine, daughter of Brigadier General Samuel Ovenshine. In 1901, he was promoted to captain and transferred from Cuba, where he has served initially as quartermaster and commissary for the 10th Cavalry Regiment, and later as aide-de-camp and adjutant-general of the department of Santiago and Puerto Principe.

After serving briefly in the Secretary of War office, he requested and received transfer to duty in the Philippines with the 11th Cavalry Regiment. He then served as Assistant Chief of the Philippine Constabulary from 1903 to 1909 and again from 1910 through 1913. By late April 1914 he was commanding the unit defending the California border at Calexico. In 1916, he was on the Mexican border with Brigadier General John J. Pershing, pursuing Pancho Villa.

When the United States entered World War I in April 1917, Harbord was attending the United States Army War College. He was selected by Pershing, now a major general appointed to command the American Expeditionary Forces (AEF), to be his chief of staff. Harbord graduated in early May, and on 28 May set sail for England with Pershing and his headquarters staff. Over the next few months Harbord worked closely with Pershing to organize the AEF's buildup on France's Western Front, including the shipping schedules of American forces being sent to Europe, and he was promoted to temporary brigadier general in August 1917.

Following a great German offensive against the Western Front on March 21, 1918, the British and French armies were in retreat, and the need for American troops was urgent. Previously agreed to arrangements to provide 120,000 servicemen a month for three months was cast aside when Pershing was informed by the British that by using confiscated Dutch shipping, over 300,000 American soldiers could be sent a month. However, due to manpower attrition within the British Expeditionary Force (BEF), its combat divisions were reduced in strength by 25%, and with the breakthrough on the front, the British were asking that only infantry and machine gun battalions be sent over, and all other units be held back, as the overwhelming need at that time was for infantrymen. The American policy on this matter was quite different: Pershing was sent to France to organize American armies under American leadership; the idea that its combat units would be used solely as replacement units, or as reinforcements, for foreign countries was unthinkable. President Woodrow Wilson would not agree to this. He thought the idea would not go over well with the American public, and it risked preventing an American army from ever being formed. In secret conversations, General Pershing even said he was willing to risk the fall of France, because the United States would still carry on the war against the Kaiser; if his forces were stripped away from him and the Allies lost, then Germany would win complete victory. For his part, Prime Minister Clemenceau thought this plan appealed to the romantic side of America's intervention.

During a Supreme War Council meeting in Versailles on March 28, President Wilson shifted his position on American ground forces by allowing the temporary duty of AEF combat units in the British and French ranks (Joint Note #18). This was confirmed in, "The London Agreement" of April 27. However, at the next Supreme War Council meeting in Abbeville, held a month later, other troops were allowed, and Pershing held that the latest agreement was in force. This brought rebuke and a letter from Prime Minister Clemenceau to President Wilson. In a follow-up conversation between Lord Reading, the British ambassador to the United States, and Harbord, the ambassador said the British would be willing to supply the transportation of 120,000 American infantry and machine gun unit personnel to France, if the United States could supply the men. Harbord says the statement was like, "the sun breaking through the clouds" because, "If Great Britain can give us the ships to carry infantry alone, she could not refuse to carry troops from any other arm of the service. Accordingly, I said to him, 'Give me the ships, and I will furnish 120,000 men a month.'" When the ships arrived, the ship captains were instructed to accept only infantry and machine gun units. When Lord Reading found out that complete divisions were assembling, he was furious. When he was told that he must have misunderstood his conversation with Harbord, it looked like a conspiracy was in the works by the American generals. As a result of this, in May 1918, General Pershing transferred out much of his staff who he said, 'were too complacent about themselves, and how things are run around here'. The first to go was Harbord, who was sent forward to the trenches to command troops in battle. However, due to Harbord's decision, the American position prevailed, and full American divisions kept coming, so much so that by the time of the Armistice, the AEF. was two million men strong, two full American armies were formed, and a third was ready and deployed to the Rhineland in January 1919. In all, 40 complete divisions had arrived, 30 were fielded, and 10 were under temporary British control. A complete list of A.E.F. divisions can be found here.