[n 1] His grandfather was Colonel Henry Clay Pratt (1814–1884), West Point Class of 1837, who had been cited for gallantry during the Mexican–American War.

[5] Pratt spent most of his career as an officer and pilot in the Army antecedents of the United States Air Force.

On August 1, 1900, Pratt enrolled at the United States Military Academy, entering the Corps of Cadets.

He served five months as an aide to Major General William Harding Carter, who had organized the Army into the Maneuver Division as a demonstration of force to revolutionaries in Mexico.

From there, Pratt reported to San Antonio, Texas, in January 1916 as aide to Brigadier General George Bell, Jr.

He accompanied Bell's headquarters to the El Paso District in support of the Punitive Expedition against Pancho Villa in Mexico.

When United States entered World War I in April, he received temporary promotion to major.

In Europe, the Air Service of the Army Expeditionary Force (AEF) organized and began combat operations, and Pratt was promoted to colonel (temporary, Signal Corps) at the end of August.

Within ten days, Pratt was on duty at the Division of Military Aeronautics (DMA) in Washington, D.C.[n 4] He was sent to Europe at the end of the first week of October, when the Meuse Argonne Offensive was underway.

On March 9, 1919, President Woodrow Wilson issued an executive order formally consolidating all military aviation functions under the Director of Air Service, Major General Charles Menoher, and Pratt was assigned to his staff on March 17 to help organize and implement a "divisional staff" system along the lines of that used by the AEF.

As acting Third Assistant Executive, he supervised the Operations and Training Group[n 5] until April, when General Billy Mitchell took over.

[n 6] This made the Air Service a statutory combatant arm of the line, enabling Pratt to transfer to that branch.

On September 25, Pratt moved up to Air Officer, Eighth Corps Area,[n 8] located at Fort Sam Houston, until April 26, 1921.

By June, he completed the student officer course at the Air Service Bombardment School at Kelly by the 2nd Group.

[9] On June 5, 1928, Pratt was assigned command of Mitchel Field, New York, and promoted to lieutenant colonel, Air Corps.

The maneuvers concluded with a live ordnance demonstration that Pratt orchestrated on the portion of the depot reservation that is now the main runway of Wright-Patterson Air Force Base.

[12] In July 1929, Pratt was transferred to Fort Shafter, to assume the duties of Air Officer for the Hawaiian Department.

Gillmore's retirement left a vacancy for Chief of the Air Corps Materiel Division, and President Herbert Hoover named Pratt to fill the position.

[15] Pratt was given command of the 2nd Wing at Langley Field, Virginia, after the War Department activated the General Headquarters (GHQ) Air Force on March 2, 1935.

[13][n 12] In December 1935, the GHQ Air Force conducted a major exercise under field conditions in which 55 of its best bombardment and attack aircraft simulated air raids on Miami, Florida, defended by 55 Boeing P-26 fighters based at Miami Municipal Airport under Pratt's direction.

[16] September 1935, politically embattled Chief of Air Corps Benjamin Foulois decided to retire in December "for the good of the service" and took his terminal leave.

The Roosevelt administration scrutinized senior Air Corps officers for a replacement, and looked at Pratt as one of its two main candidates.

"He [Pratt] has greater mental ability than others on the list," noted Secretary of War George Dern to Roosevelt, "but it is possible that he is not as cooperative as Westover."

[20] Pratt served as interim commander of the Philippine Division twice: from July 25, 1939, to November 1939, when Major General Walter S. Grant was advanced to command of the Philippine Department; and from May 31, 1940, to the end of his own tour on November 6, 1940, replacing Major General George Grunert.

[21] These two terms makes Pratt the only person to command both a U.S. Air Force wing and an army division.

[22] He was carried on the retired list of the United States Air Force in the rank of major general.