Eaker remained with the 64th Infantry until March 1918, when he was placed on detached service to receive flying instruction at Austin and Kelly Fields in Texas.

Meanwhile, on July 1, 1920, he was commissioned into the Regular Army as a captain in the Air Service and returned to the United States in January 1922, for duty at Mitchel Field, New York, where he commanded the 5th Aero Squadron and later was post adjutant.

In June 1924, Eaker was named executive assistant in the Office of Air Service at Washington, D.C., and from December 21, 1926, to May 2, 1927, he served as a pilot of one of the Loening OA-1 float planes of the Pan American Goodwill Flight that made a 22,000 mile (35,200 km) trip around South America and, with the others, was awarded the Mackay Trophy.

For this achievement the entire crew of five, including Eaker and mission commander Major Carl Spaatz, were awarded the DFC.

In the summer of 1935, he was detached for duty with the Navy and participated aboard the aircraft carrier USS Lexington, on maneuvers in Hawaii and Guam.

During his time at Ft Leavenworth from June 3–7, 1936, Eaker made the first blind (instruments only) transcontinental flight from New York to Los Angeles.

Eaker's position as commander of the Eighth Air Force led to his becoming the model for the fictional Major General Pat Pritchard in the 1949 movie Twelve O'Clock High.

He personally participated in the first US B-17 Flying Fortress bomber strike against German occupation forces in France, bombing Rouen on August 17, 1942.

[4] Eaker also strongly advocated work on improving the range of escort fighters using drop tanks,[4] so that his Republic P-47 Thunderbolts could stay with the bomber formations for longer periods.

He did not approve of the plan to bomb Monte Cassino in February 1944, considering it a dubious military target, but ultimately signed off the mission and gave in to pressure from ground commanders.

Historians of the era now generally believe Eaker's skepticism was correct and that the ancient abbey at Monte Cassino could have been preserved without jeopardizing the allied advance through Italy.

He personally led the first raid of Operation Frantic on 2 July 1944, flying in a B-17 called Yankee Doodle II and landing at a Soviet base at Poltava in Ukraine.

Goldwater had originally wanted to simply promote Jimmy Doolittle to four star rank, but was told by Air Force Secretary Verne Orr that this would put Eaker in an awkward position because he "had greater responsibilities during World War II.

[8] However, the legislation stalled in the House, which prompted Goldwater to only seek confirmation via the Senate, which was arguably unlawful because of statutory restrictions on general officers that required them to be in active service.

Criticizing a prominent military leader so soon after World War II likely had a negative effect on Stevenson's turnout in the election, and in Howard County in particular (which had quartered an Army Air Force Bombardier School during World War II) returned an abnormally high net gain for Johnson as compared to his gains in other areas.

On September 26, 1978, the U.S. Congress passed, and on October 10, 1978, President Jimmy Carter signed, Public Law 95-438, which awarded the Congressional Gold Medal to General Eaker, "in recognition of his distinguished career as an aviation pioneer and Air Force leader".

[12] Eaker died August 6, 1987, at Malcolm Grow Medical Center, Andrews Air Force Base, Maryland, and is buried in Arlington National Cemetery.