McNair's experience of more than 30 years with equipment and weapons design and testing, his administrative skills, and his success in the areas of military education and training led to his World War II assignment as commander of Army Ground Forces.

While historians continue to debate some of McNair's decisions and actions, including the individual replacement system for killed and wounded soldiers, and a controversy over the use of tanks or tank destroyers as anti-tank weapons, his concentration on advanced officer education, innovative weapons systems, improved doctrine, realistic combat training, and development of combined arms tactics enabled the Army to modernize and perform successfully on the World War II battlefield, where the mobility of mechanized forces replaced the static defenses of World War I as the primary tactical consideration.

He was killed by friendly fire while in France to act as commander of the fictitious First United States Army Group, part of the Operation Quicksilver deception that masked the actual landing sites for the Invasion of Normandy.

[8] While he was on the Naval Academy waiting list as an alternate,[12] he began studies at the Minnesota School of Business in Minneapolis, where he concentrated primarily on mechanical engineering and statistics courses.

[27] Initially, McNair's Ordnance testing centered on improving the mountain guns used by units including his 12th Battery for artillery support of troops in rugged terrain where limbers and caissons could not travel.

[28] In this posting, he gained experience with both laboratory and practical methods of experimentation, including analyzing bronze, steel, and cast iron to determine the best materials to use in manufacturing cannons and other weapons.

[31] Jacob L. Devers, who was assigned to Battery C after his 1909 West Point graduation, recalled McNair as an outstanding commander who set a superior personal example, and knew how to motivate his subordinates to perform to a high standard.

[34] McNair's skills in technical drawing, engineering, prototype building, and statistical analysis began to be known Army-wide; in 1912 the commandant of the Field Artillery School requested him by name for assignment to his staff.

He continued to impress his superiors with his technical and tactical expertise, and at the end of the war he received the Army Distinguished Service Medal from General John J. Pershing, the Commander-in-Chief (C-in-C) of the AEF, and the French Legion of Honor (Officer) from Philippe Pétain.

[54] Assigned to the project by Hawaiian Department commander Major General Charles Pelot Summerall because of his reputation for objectivity in carrying out analysis and experimentation with military weapons and equipment, McNair created a committee made up of himself, two coast artillery officers, and an aviation officer to investigate the strengths and weaknesses of the two branches, especially with regard to defending Army and Navy bases on Oahu, and make recommendations on the best way to employ coast artillery and military aircraft.

[56] Coe concluded his argument by recommending that the McNair board's findings be approved by the Army as its official position on the issue of coastal artillery versus bombers for shore defense.

[57] McNair's involvement in the issue continued during the 1925 court-martial of Brigadier General Billy Mitchell, whose zealous advocacy of creating a separate Air Force resulted in accusations of insubordination.

[65] Purdue's president, Edward C. Elliott, was a strong advocate at the national level for ROTC, and a leading voice in opposition to the pacifist movement which gained strength and influence following World War I.

[67] McNair's leadership, technical expertise, and administrative abilities resulted in enhanced student participation and improved morale, and developed the program into the Army's largest light artillery unit.

In the 1920s the curriculum had been revised so that the program of instruction concentrated on economic, industrial, and logistics issues related to large-scale wartime mobilizations, as well as the doctrine, strategy, and tactics requirements associated with organizing, training, deploying, and employing large scale units for combat (typically division and above).

[70] Among his classmates were several officers who became prominent during World War II, including: Simon Bolivar Buckner Jr.,[71] Roy Geiger,[72] Oscar Griswold,[73] Clarence R. Huebner,[74] Troy H. Middleton,[75] and Franklin C.

[79] In this position, he worked with the school's Gunnery Department to address field artillery doctrine issues that had lingered since World War I, including limited mobility, inadequate communications, and overly detailed fire direction techniques.

[79] Successive Gunnery Department directors Jacob Devers, Carlos Brewer, and Orlando Ward recognized that continuing improvement to innovations including machine guns and tanks made the static trench warfare of World War I unlikely to be repeated.

In addition, they pioneered techniques to enhance accuracy, including forward observers (FOs) who could direct rounds onto targets based on seeing their impact, rather than the unobserved timed fire and rolling barrages that had prevailed in World War I.

[81] In addition, McNair benefited from the experience of working with civilian government leaders to plan and direct CCC activities, which was also put to good use in his later assignments as one of the Army's highest-level commanders.

[87] In his annual performance appraisal, his division commander, Major General James K. Parsons, rated McNair as superior, and recommended him for assignment as a corps or army chief of staff.

[122] A variety of other factors, including the entry of the Soviet Union into the war on the side of the Allies after Adolf Hitler broke his non-aggression pact with Joseph Stalin by launching Operation Barbarossa, the need to ensure that enough farmers and agricultural workers were available for food production, and the need to maintain a U.S. workforce large enough to handle the production of weapons, vehicles, ammunition, and other equipment caused Army Chief of Staff Marshall to decide that maintaining the Army's ground combat strength at 90 divisions would strike the balance between too few soldiers to defeat the Axis powers, and so many that there were not enough civilians in the U.S.

[127] Overall, the Army's wartime division organization and reorganizations have been judged a success by historians, in that they provided an adequate number of units to win the war, while ensuring that agricultural and industrial production could continue.

[136] In another effort to inform the public of the Army's personnel needs and improve the way the AGF was perceived, on Armistice Day in November 1942, McNair delivered a radio address over the Blue Network.

[137] In his remarks, titled "The Struggle is for Survival", McNair described the fighting capability and ruthless attitude of soldiers in the Japanese and German armies, and stated that only similar qualities in American ground troops – by implication, meaning not "the more genteel forms of warfare" practiced by the AAF and ASF – would see the Allies through to victory.

[142] Based on difficulties with completing training, in large part because the abilities of the recruits were lagging as a result of having grown up in the segregated education system and culture then prevalent in the United States,[140] McNair advocated for separate battalions of African American soldiers, arguing that they could be more effectively employed in this manner.

[152] Over time, commanders in combat resorted to field expedient measures to solve the problems, including learning to employ anti-tank guns and later tank destroyers in mutually supporting positions, and integrating them with infantry and armor units to maximize their effectiveness as part of a combined arms effort.

[155] McNair opposed this request, still convinced that smaller but heavily armed self-propelled tank destroyers could be employed faster and more effectively, especially when considering factors such as available space on cargo ships transporting weapons and equipment to Europe.

[180] Another enduring McNair legacy was his training method of beginning with basic soldier skills and then building through successive echelons until large units became proficient during exercises and war games that closely simulated combat.

[204] She traveled to several foreign locations, including North Africa, Europe, and Latin America to interview employees and observe working conditions in order to make recommendations for improvements.