General of the Air Force Henry Harley "Hap" Arnold (June 25, 1886 – January 15, 1950) was an American five-star general officer holding the grades of General of the Army and later General of the Air Force. He is the only officer to ever hold a five-star grade in two different U.S. military services. Arnold was an aviation pioneer and the Chief of the United States Army Air Corps (from 1938), the Commanding General of the U.S. Army Air Forces (from 1941 until 1945), and the only five-star General of the Air Force (starting in 1949).

Instructed in flying by the Wright Brothers, Arnold was one of the first military pilots worldwide, and the second rated pilot in the history of the United States Air Force. He overcame a fear of flying that resulted from his experiences with early flight, oversaw the expansion of the Air Service during World War I, and became a protégé of Gen. Billy Mitchell, all of which at times nearly ended his aeronautical career. Arnold became a powerful advocate for creation of an independent Air Force and played a key role in the political struggles over it with the hierarchies of the United States Army and United States Navy. He rose to command the Army Air Forces immediately prior to U.S. entry into World War II and directed its expansion into the largest and most powerful Air Force in the world. An advocate of technological research and development, Arnold's tenure saw the development of the intercontinental bomber, the jet fighter, the extensive use of radar, global airlift and atomic warfare as mainstays of modern air power.

Born June 25, 1886, in Gladwyne, Pennsylvania, Arnold was the son of a strong-willed physician who also served in the Pennsylvania National Guard and was a member of the prominent political and military Arnold Family. Henry Arnold was Baptist in religious belief, but had strong Anglican ties through his father's family. Arnold attended Lower Merion High School in Ardmore, Pennsylvania, graduating in the class of 1903. The Athletic fields at Lower Merion are named after him. Arnold took the examination for entrance into West Point after his brother Thomas (already a student at Pennsylvania State University) refused to do so, but placed second on the list. He received a delayed appointment when the nominated cadet confessed to being married, counter to academy regulations.

Arnold entered the United States Military Academy in the summer of 1903 at age 17. At the academy he helped found the "Black Hand", a cadet group of pranksters. He wanted to join the cavalry but an inconsistent demerit record and an academic class standing of 66th out of 111 cadets resulted in his being commissioned on June 14, 1907, as a Second Lieutenant, Infantry, an assignment he initially protested, but was persuaded to accept (there was no definite commissioning requirement for USMA graduates in 1907). He was commissioned into the 29th Infantry Regiment (United States), then stationed in the Philippines.

There, disliking the infantry, Arnold volunteered to assist Capt. Arthur S. Cowan of the Army Signal Corps in a military cartography detail, mapping the entire island of Luzon. Cowan returned to the United States in January 1909, to become the chief of the newly created Aeronautical Division, U.S. Signal Corps and to recruit two lieutenants to become pilots. Cowan contacted Arnold, who cabled his interest in a transfer to the Signal Corps but heard nothing in reply for two years. In June 1909, the 29th Infantry was relocated to Fort Jay, New York. In 1911, Arnold applied for transfer to the Ordnance Department because it offered an immediate promotion to First Lieutenant. While awaiting the results of the competitive examination he had taken for the position, he learned that his interest in aeronautics had not been forgotten.

Arnold immediately sent a letter requesting a transfer to the Signal Corps, and on April 21, 1911, received Special Order 95, detailing him and 2nd Lt. Thomas D. Milling of the 15th Cavalry, to Dayton, Ohio, for a course in flight instruction at the Wright brothers' aviation school at Simms Station, Ohio. Beginning instruction on May 3, Arnold made his first solo flight May 13 after three hours and forty-eight minutes of flying lessons (Milling had already soloed on May 8 with two hours of flight time). In June he and Milling completed their instruction. Arnold received Fédération Aéronautique Internationale (FAI) pilot certificate No. 29 on July 6, 1911, and Military Aviator Certificate No. 2 a year later. He also was recognized by General Order No. 39, dated May 27, 1913, as one of the 24 original military aviators and authorized wear of the newly designed Military Aviator badge. This was the original suspended eagle design. While soon replaced by the more familiar aviator wings; Arnold wore both types throughout his career.

Arnold and Milling were sent to the Aeronautical Division, U.S. Signal Corps at College Park, Maryland, as the Army's first flight instructors on June 14. There Arnold set an altitude record of 3,260 feet (990 m) on July 7 and twice broke it (August 18, 1911, to 4,167 feet (1,270 m); and June 1, 1912, 6,540 feet). In August 1911, he experienced his first crash, trying to take off from a farm field after getting lost. In September Arnold became the first U.S. pilot to carry mail, flying a bundle of letters five miles (8 km) on Long Island, New York.

The flight school moved by train to Augusta, Georgia, in November 1911, hoping to continue flying there during the winter, but their flying was limited by rain and flooding, and they returned to Maryland in April 1912. Arnold accepted delivery of the Army's first plane with a propeller and engine mounted on the front on June 26, but crashed into the bay at Plymouth, Massachusetts, during takeoff. Arnold began to develop a phobia about flying, intensified by the earlier fatal crash of the Wright Company instructor who taught him, Arthur L. Welsh (1881 – 1912), at College Park on June 12. Another fatal crash occurred at College Park on September 18, involving an academy classmate of Arnold's, 2d Lt. Lewis Rockwell (1887 – 1912).

In October, Arnold and Milling were ordered to enter the competition for the first MacKay Trophy for "the most outstanding military flight of the year." Arnold won when he located a company of cavalry from the air and returned safely, despite high turbulence. As a result he and Milling were sent to Fort Riley, Kansas, to experiment with spotting for the field artillery. On November 5 his plane stalled, went into a spin, and he narrowly avoided a fatal crash. He immediately grounded himself voluntarily and applied for a leave of absence. Flying was considered so dangerous that no stigma was attached for refusing to fly, and his request was granted (five of the Army's 14 aviators transferred out during 1913). During his leave of absence he renewed an acquaintance with Eleanor "Bee" Pool, the daughter of a banker, and one of his father's patients.

On December 1, Arnold took a staff assignment as assistant in the Office of the Chief Signal Officer in Washington, D.C. with the task of closing the flying school at College Park. Although promoted to 1st lieutenant on April 10, 1913, Arnold was unhappy and requested a transfer to the Philippines. In August, after his first request had been denied for lack of a vacancy, he returned to the infantry.

On September 10, 1913, he married Eleanor Pool, with Lt. Milling acting as his best man. Sent back to the Philippines in January 1914, he was quartered adjacent to 1st Lt. George Catlett Marshall, who became his mentor, friend and life-long supporter. Soon after their arrival Bee miscarried, but on January 17, 1915, their first child, Lois Elizabeth Arnold, was born at Fort McKinley, Manila. In January 1916, completing a two-year tour with the 13th Infantry, Arnold was transferred to the 3rd U.S. Infantry and returned to the United States. En route, he received a telegram in Hawaii from Major William L. Mitchell, whom he had met in 1912 at College Park and who was now executive officer of the Air Service, offering him the rank of captain if he volunteered for a return to aviation. On May 20, 1916, Arnold was promoted to Captain (temporary) and reported to Rockwell Field (named for his academy classmate, Lewis Rockwell) for duty as a supply officer with the Aviation Section, U.S. Signal Corps.

Between October 18 and December 16, 1916, Arnold, encouraged by former associates, worked to overcome his fear of flying with voluntary extra duty flying fifteen to twenty minutes a day. On November 26, he flew solo for the first time in four years, and on December 16 he performed aerobatics. Before he could be reassigned to flying duties, he was involved as a witness in a controversial incident. A senior officer at Rockwell had authorized an unofficial excursion flight for a non-aviator that resulted in the loss of the airplane. After testifying to army investigators, Arnold was transferred to Panama by the officer he testified against, one day after the birth of his second child, Henry H. Arnold, Jr., on January 29, 1917.

Arnold was ordered to find a suitable location for an airfield in the Panama Canal Zone, then build it and command the just forming 7th Aero Squadron. When the military services could not agree on a site, Arnold was ordered to Washington D.C. to resolve the dispute, and was en route by ship when the United States declared war on Germany. Arnold requested to be sent to France, but his presence in Washington worked against him, since the Aviation Section now needed qualified officers for headquarters duty. He was immediately given temporary duty as chief of the Information division with a temporary promotion to major on June 27.

On August 5, 1917, he was again promoted and became the youngest full colonel in the Army (Arnold was a Colonel, Signal Corps — for a period of time he also held the concurrent brevet rank of Major, Infantry), in preparation for being named executive officer of the Aviation Section ten days later. He spent the next year trying to implement a large aviation appropriations bill over the resistance of the Army General Staff. Although he largely failed, Arnold gained significant experience in aircraft production and procurement, the construction of air schools and airfields, and the recruitment and training of large numbers of personnel, as well as learning political in-fighting in the Washington environment, all of which helped him significantly 25 years later.

Arnold's third child, William Bruce Arnold, was born July 17, 1918. Shortly after, Arnold arranged to go to France to brief the commander of the American Expeditionary Force, General John Pershing, on new developments. Aboard a ship to France in late October he developed influenza and was hospitalized on his arrival in England. He did reach France in 1918, but the Armistice ended the war on November 11, 1918.

The improvements in aircraft during the war and the creation of organizations such as the National Advisory Committee for Aeronautics improved the potential for United States Army airpower, and it had been made a branch separate from the Signal Corps on May 14, 1918. However to keep control of aviation in the Army ground forces, the first post-war Chief of the reorganized Air Service, Maj. Gen. Charles T. Menoher, was an infantry general who had commanded the 42nd "Rainbow" Infantry Division in France. He was succeeded by another non-aviator, Maj.Gen. Mason Patrick from the Corps of Engineers, who General John Pershing had used to head the Air Service of the American Expeditionary Force.

Arnold was ordered back to Rockwell Field on December 21, 1918, to supervise the demobilization of 8,000 airmen and surplus aircraft. He worked hard to preserve and promote aviation with shows and publicity stunts. At Rockwell Field Arnold first established relationships with the men that would become his main aides, his executive officer, Captain Carl Spaatz and his adjutant, 1st Lt. Ira Eaker, while supporting the highly visible efforts of Brig. Gen. William L. Mitchell. He was promoted to the permanent rank of Captain on June 30, 1920, and the permanent rank of Major the next day, July 1.

After demobilization Rockwell became a remote outpost of the service. Arnold experienced several serious illnesses and accidents requiring hospitalization. His fourth child, John, was born in the summer of 1921, and died on June 30, 1923, of acute appendicitis.

In August 1924, Arnold was unexpectedly assigned to attend the Army Industrial College. After completing the course he was reassigned to duty as Chief of Air Service information in January 1925, working closely with Brig. Gen. Mitchell. When Mitchell was court martialed, Arnold, Spaatz, and Eaker were all warned that they were jeopardizing their careers by vocally supporting Mitchell, but they testified on his behalf anyway. After Mitchell was convicted on December 17, 1925, Arnold continued to use his position in the Information Office to provide propaganda to airpower friendly journalists in defiance of orders from the General Staff and with the knowledge of General Patrick. In February 1926, Secretary of War Dwight F. Davis ordered Patrick to discipline the leakers, and Patrick chose Arnold, with whom he shared a mutual dislike. Arnold was given the choice of resignation from the Army or a general court martial, but when Arnold chose the latter, the Army apparently decided it did not want another public fiasco, and instead transferred Major Arnold to command the 16th Observation Squadron at Fort Riley, Kansas — a cavalry post far from aviation advances. On February 24, 1927, his son David Lee Arnold was born at Fort Riley.

Arnold accepted his exile and in May 1927, participated in war games at Fort Sam Houston, Texas. There he met Maj. Gen. James E. Fechet, who had succeeded Patrick as head of the service, now the U.S. Army Air Corps, and successfully completed a difficult assignment for him. During this period Arnold wrote six books of juvenile fiction whose purpose was to encourage young people to fly. General Fechet intervened with Army Chief of Staff General Charles P. Summerall to have Arnold's exile ended by assigning him to the Army's Command and General Staff School at Fort Leavenworth. The year-long course was highly unpleasant for Arnold because of doctrinal differences with the school's commandant, but Arnold graduated with high marks in June 1929. His next assignment was commander of Fairfield Air Service Depot, Ohio. In 1930 he also became executive officer of the Air Materiel Division, and was promoted to lieutenant colonel on February 1, 1931.

On November 27, 1931, he took command of March Field, California. The assignment included the refurbishing of the base into one of the showcase installations of the Air Corps and required that he resolve strained relations with the citizens of Riverside, California. He accomplished this by having his officers join at least one of the local social service organizations and by a series of well-publicized relief efforts. While base commander at March Field, personnel under Arnold's command flew food drops during blizzards in the winter of 1932-33, assisted in relief work during the Long Beach earthquake of March 10, 1933, and established a camp for 3,000 boys of the Civilian Conservation Corps. In September 1933, Arnold designated a portion of the Rogers Dry Lake near Muroc as a training site for his March Field squadrons. This site would become today's Edwards Air Force Base.

In 1934, he commanded one of the three military zones during the Air Mail scandal, but his pilots performed well and his own reputation was relatively untouched by the fiasco. Later that same year he won his second Mackay Trophy, when he led ten of the new B-10 bombers on an 8,290-mile (13,340 km) flight from Washington to Fairbanks, Alaska, and back. Although he lobbied for recognition of the other airmen involved in the Alaska flight, the Army Chief of Staff ignored Arnold's recommendations, with the result that his reputation among some of his peers was tarnished by resentment.

On March 1, 1935, General Headquarters (GHQ) Air Force was activated to take control of all combat aviation units of the Air Corps based in the United States. Its first commander, Major General Frank Andrews, tapped Arnold to command its First Wing, headquartered at March Field, and he was promoted to the temporary rank of brigadier general on March 2, 1935.

On December 28, 1935, Arnold was summoned to Washington by the Army Chief of Staff, General Malin Craig, and over his protests, was made Assistant Chief of the Air Corps under its new Chief, Major General Oscar Westover. Instead of commanding operational units, Arnold was now in charge of procurement and supply. Westover was killed in an air crash on September 21, 1938, and Arnold then became Chief of the Air Corps, with an immediate promotion to Major General on September 22. This move did not return Arnold to the operational Air Force, but it did empower him to plan for expansion of the Air Corps into a branch of the Army co-equal with the ground forces.

His first move was to encourage research and development efforts, particularly the B-17 and the concept of Jet-assisted takeoff. To encourage the use of civilian expertise, the California Institute of Technology became a beneficiary of Air Corps funding and Theodore von Kármán of its Guggenheim Aeronautical Laboratory developed a good working relationship with Arnold that led to the creation of the Scientific Advisory Group in 1944. Charles Lindbergh was also briefly co-opted by the Air Corps as a spokesman for aviation. Arnold concentrated on rapid returns from R&D investments, exploiting proven technologies to provide operational solutions to counter the rising threat of the Axis Powers. From 1940 onward, Arnold also pushed for jet propulsion, especially after the British shared their plans of Whittle's turbojet in 1941.

With U.S. participation in the Second World War inevitable, the division of authority between the Air Corps and General Headquarters Air Force was removed with a revision of Army Regulation 95-5 that created the United States Army Air Forces on June 20, 1941. Arnold was made Chief of the Army Air Forces and acting Deputy Chief of Staff for Air with command authority over both the Air Corps and Air Force Combat Command (successor to GHQ Air Force). This also provided the air arm with a staff of its own, brought the entire organization under the command of one general (Arnold), and granted it near autonomy. It also by consensus postponed debate on separation of the Air Force into a service co-equal with the Army and Navy until after the war.

Arnold gave the new Air Staff as its first assignment the development of a war plan for fighting both Germany and Japan, and it produced "Air War Plans Division — Plan 1" (AWPD-1), which became the basis for air strategy during the war. AWPD-1 defined four tasks for the USAAF: defense of the Western Hemisphere, an initial defensive strategy against Japan, a strategic air offensive against Germany, and a later strategic air offensive against Japan in prelude of invasion. It also planned for an expansion of the USAAF to 60,000 aircraft and 2.1 million men. AWPD-1 called for 24 groups (approximately 750 airplanes) of B-29 very heavy bombers to be based in Northern Ireland and Egypt for use against Nazi Germany, and for production of sufficient Consolidated B-36s for intercontinental bombing missions of Germany. Even before then he had pushed for aid to Britain; with U.S. entry into the war, Arnold, a strong supporter of strategic bombing, closely supervised the creation of the Eighth Air Force in England to limit the diversion of Army bombers to anti-submarine patrol and to the Pacific Theater, and thwart British lobbying to have U.S. bombers sent as individual replacements for the Royal Air Force.

In the wake of U.S. entry in the war, Arnold was promoted to lieutenant general on December 15, 1941. On March 9, 1942, the issuance of War Department Circular 59 granted the USAAF full autonomy, equal to and entirely separate from the Army Ground Forces and Services of Supply. The office of the Chief of the Air Corps and the Air Forces Combat Command were eliminated entirely, and Arnold became Commanding General of the USAAF and a member of both the Joint Chiefs of Staff and the Combined Chiefs of Staff.

In response to an inquiry from the U.S. President Franklin D. Roosevelt, Arnold directed the Air War Plans Division in August 1942, to revise its estimates and AWPD-42 was issued, calling for 75,000 aircraft and 2.7 million men, but also adding a call for 8,000 gliders and the production of 8,000 aircraft for use by other allies. AWPD-42 reaffirmed earlier strategic priorities, but increased the list of industrial targets from 23 to 177, ranking the German Luftwaffe first and its submarine force second in importance of destruction. It also directed that the B-29 bomber not be employed in Europe because of problems in its development, but instead that the B-29 program's deployment be concentrated in the Far East to destroy the Japanese military power.

Immediately after the attack on Pearl Harbor Arnold began to carry out AWPD-1. The primary strategic bombing force against Nazi Germany would be the Eighth Air Force, and he named General Spaatz to command it and General Eaker to head its Bomber Command. (Arnold and Eaker had written three books together.) Other Arnold protégés eventually filled key positions in the strategic bombing forces, including Generals Frank A. Armstrong, Newton Longfellow, Haywood S. Hansell, Laurence S. Kuter, Laverne Saunders, Emmitt O'Donnell and James H. Doolittle.

Despite protecting his strategic bombing force from demands of other services and allies, Arnold was forced to divert resources from the Eighth to support operations in North Africa, crippling the Eighth in its infancy and nearly killing it. Eaker (now Eighth Air Force commander) found from experience that the pre-war doctrine of daylight precision bombing, developed at the Air Corps Tactical School as a foundation for separating the Air Force from the Army as an equal service, had erred in its tenet that heavily armed bombers could penetrate all defenses to reach any target without the support of long-range escort fighters. Early in 1943 he began requesting more fighters and jettisonable fuel tanks to increase their range, in addition to repeated requests to increase the size of his small bombing force. Eaker was resisted not only by opponents of strategic daylight bombing but by his fighter commanders as well, who argued that the use of drop tanks would endanger their aircraft. Heavy losses in the summer and fall of 1943 on deep penetration missions increased Eaker's requests. Arnold, under pressure and impatient for results, ignored Eaker's findings and placed the blame on a lack of aggressiveness by bomber commanders. This came at a time when General Dwight D. Eisenhower was putting together his command group for the invasion of Europe, and Arnold approved Eisenhower's request to replace Eaker with his own commanders, Spaatz and Doolittle. Ironically, the very items Eaker requested — more airplanes, drop tanks, and P-51 fighters — accompanied the change of command and made the Eighth Air Force decisive in defeating Germany using the daylight bombing doctrine.

With the strategic bombing crisis resolved in Europe, Arnold placed full emphasis on completion of the development and deployment of the B-29 to attack Japan. The B-29 program had been plagued with a seemingly unending series of development problems, subjecting it and Arnold to much criticism in the press and from skeptical field commanders. The B-29 was the key component of the AAF's fourth strategic priority, since no other land based bomber was capable of reaching the Japanese homeland, but by February 1944, the XX Bomber Command, slated to begin Operation Matterhorn on June 1, had virtually no flight time yet above an altitude of 20,000 feet (6,100 m). With a designated overseas deployment date of April 15, 1944, Arnold intervened in the situation personally by flying to Kansas on March 8. For three days he toured training bases involved in the modification program, distressed at his findings of shortages and work failures, and on the spot made a military procurement officer accompanying him, Maj.Gen. Bennett E. Meyers, coordinator of the program. Meyers (who would after the war be investigated by Congress in a procurement scandal in which Arnold was compelled to testify), succeeded in the "Battle of Kansas": despite labour problems and blizzard weather a complete bomb group was ready for deployment by April 9. The mechanical problems of the B-29, however, had not been resolved, and combat operations identified many new ones. Arnold felt the pressure of not only achieving the goals of AWPD-1, but of justifying by results a very expensive technological project in the B-29, and also the highly classified knowledge that the B-29 would be called upon to deliver the atomic bomb, if the Manhattan Project succeeded. Operations against Japanese targets in China and Southeast Asia began in June, 1944 and from the outset produced far less positive results than expected.

In many ways the difficulties of the Twentieth Air Force's campaign against Japan mirrored those of the Eighth Air Force's against Germany. With characteristic impatience, Arnold quickly relieved Brig. Gen. Kenneth Wolfe, the B-29 commander in China, and replaced him with Maj.Gen. Curtis LeMay. A second B-29 bomber command began operations from bases in the Mariana Islands in November. Brig. Gen. Haywood S. Hansell, one of the architects of AWPD-1 and AWPD-42, commanded XXI Bomber Command but encountered even more command problems than had Wolfe or LeMay. After two months of poor results, and because he resisted a campaign of firebombing attacks against Japanese population favored by Arnold and his chief of staff, Lauris Norstad, Arnold decided he too needed replacing. He shut down operations from China, consolidated all the B-29s in the Marianas, and replaced Hansell with LeMay in January 1945. Arnold made himself commanding general of the Twentieth Air Force, for which he is sometimes criticized for failure to delegate. This unique command arrangement may also have contributed to his health problems (see below), but after the negative experience of building an effective bombing force against Germany, and realizing the consequences of failure against Japan, Arnold may have considered that administrative decisions regarding command could best be handled personally. However, theater commanders Gen. Douglas MacArthur, Chester Nimitz, and Joseph Stillwell all coveted the B-29s for tactical operations, to which Arnold was adamantly opposed as a diversion from strategic policy. He convinced not only Army Chief of Staff George C. Marshall, but also Chief of Naval Operations Ernest J. King, that the Twentieth was unique in that its operations cut across the jurisdiction of all three theaters, and thus should report directly to the Joint Chiefs with Arnold acting as their executive agent.

Between 1943 and 1945 Arnold experienced four heart attacks severe enough to require hospitalization. In addition to being by nature intensely impatient, Arnold considered that his personal presence was required wherever a crisis might be, and as a result he traveled extensively and for long hours under great stress during the War, aggravating what may have been a pre-existing coronary condition. A lesser but more frequent factor may have been his difficulty in handling inter-service politics, particularly with the Navy, which steadfastly refused to recognize him as a Chief of Staff. Arnold's first heart attack occurred February 28, 1943, just after his return from a lengthy and exhausting trip to the Casablanca Conference in Africa and to China. He was hospitalized at Walter Reed Army Hospital for several days, then took three weeks leave at the Coral Gables Biltmore Hotel in Florida, which had been converted into a convalescent hospital. U.S. Army regulations then required that he leave the service, but President Roosevelt waived the requirement in April after he demonstrated his recovery, and on the condition that the President be provided with monthly updates on Arnold's health. Arnold's second heart attack occurred just a month later, on May 10, 1943, and resulted in a 10-day stay in the Walter Reed Hospital. His third heart attack, less severe than the first two, occurred exactly a year later, on May 10, 1944, under the strain of the B-29 problems. Arnold took a month's leave, returning to duty in flying to London for a conference on June 7, 1944. Arnold's last wartime heart attack came on January 17, 1945, just days after he had replaced Gen. Hansell with Gen. LeMay. Arnold had not gone into his office for three days, and he refused to admit the Air Force's chief flight surgeon to his quarters to be checked up on. The flight surgeon enlisted an Army General and a personal friend of Arnold's to inquire on his condition, after which Arnold was again flown to Coral Gables, Florida, and placed under 24-hour care for nine days. Arnold again was allowed to remain in the service, but under conditions which amounted to light duty. This included a tour of European air bases. Arnold was visiting the 456th Bomb Group in Italy when he received the news of the German surrender on 7–8 May 1945.

On March 19, 1943, Arnold was promoted to a full General in the USAAF, and on December 21, 1944, he was appointed as a five-star General of the Army, placing him fourth in the U.S. Army rank structure, just behind Generals George C. Marshall, Douglas MacArthur, and Eisenhower. Becoming a five-star General or Admiral is a lifetime appointment in the American military services, and thus, there is never an official retirement from this position. Among other things, the officer draws his full salary and benefits for life and is given a small staff of officers and enlisted men as his aides.

In 1945, Arnold founded the Project RAND, which later became the non-profit think tank the RAND Corporation, with $10,000,000 of funding leftover from World War II. Initially tasked with studying military strategy, RAND has since been widely expanded in its scope beyond its original mission.

After a trip to South America in January 1946, in which he developed a heart arrhythmia severe enough to cancel the remainder of the trip, General Arnold left active duty in the USAAF on February 28, 1946, (his official date of his departure from active duty was 30 June 1946). He was succeeded by General Carl Spaatz, who also became first Chief of Staff of the United States Air Force when the US Air Force became a separate service on September 18, 1947.

Arnold retired to a 40-acre (160,000 m²) ranch near Sonoma, California, and he signed a contract with Harper & Brothers to write his memoirs. Unlike Gen. George S. Patton, an independently well-to-do officer in the U.S. Army, and his colleagues who had taken other positions (e.g., George C. Marshall was appointed as the Secretary of State by President Harry S Truman), Arnold was not healthy enough to do so and he had no source of income other than his military pension and, later, his full salary. (When promoted to the rank of General of the Air Force he received his full pay and benefits, since all five-star Generals and Admirals are on a lifetime appointment.) Arnold's autobiography was an attempt to provide financial security for his wife after his death — much like the former General and President Ulysses S. Grant who also wrote his memoirs while suffering from a fatal illness. Arnold was in the midst of writing the book when he suffered his fifth serious heart attack in January 1948, hospitalizing him for three months. However, he did later complete the book, entitled Global Mission, before his death in 1950.

On May 7, 1949, Arnold was honored by being made the first — and to date, only -- General of the Air Force. He is also the only American to serve in five-star rank in two U.S. military services. He died on January 15, 1950, at his home in Sonoma. He was given a state funeral in Washington, D.C. that included rare services held in Arlington Memorial Amphitheater, and he was buried in Section 34 of Arlington National Cemetery.

The source of his nickname "Hap" was short for "Happy," a nickname his aunt came up with. His West Point nickname was "Pewt", and possibly also "Benny", and he was known to his family as Harley during his youth. To his immediate subordinates and headquarters staff he was referred to as "The Chief."

The Arnold Engineering Development Center and Arnold Air Force Base, in Tennessee, is the world's largest and most advanced aeronautical testing and research base, and it is named for General Arnold. The top honorary organization in Air Force ROTC, the Arnold Air Society, is named in his honor, as is the cadet social center at the United States Air Force Academy, Arnold Hall. The Air Force Aid Society awards a scholarship in his name to the dependents of Air Force members or retirees. The second achievement award in the Civil Air Patrol cadet program is also named after him. Arnold appointed Marshall K. Wood in 1942 to head up the first use of the first UNIVAC in the government as part of an overall system designed to decrease pilot deaths by optimizing training and procurement. The United States Department of Defense high school at the former Wiesbaden Air Base in Wiesbaden, Germany, was renamed General H.H. Arnold High School in 1955. The school remains open to this day with the same name, even with Wiesbaden switching from an Air Force installation to an Army base. On November 7, 1988, the United States Postal Service released the H.H. "Hap" Arnold 65 cent postage stamp bearing the likeness of Arnold, in his honor, as part of the Great Americans series. The Air Force Research Laboratory generally recognizes Arnold as the visionary who first articulated that superior research and development capabilities are essential to deterring and winning wars. Arnold's ideas underpin the Laboratory's modern-day role within the Air Force. On May 18, 2006, the United States Department of the Air Force unveiled two prototypes of new service dress uniforms, one resembling the stand collar uniform worn by U.S. Army Air Corps officers prior to 1935, called the "Billy Mitchell heritage coat," and another, resembling the Army Air Force's Uniform of World War II, albeit in contemporary Air Force blue fabric, and named the "Hap Arnold heritage coat." Arnold also changed the regulation flight jacket for Air Force pilots: the celebrated leather A-2 jacket was replaced by a sage-green nylon jacket, which was easier to procure but less popular with the wearers. The A-2 was restored to uniform status in USAF in 1988.

All three of Arnold's surviving sons served as colonels in the United States Air Force. All were also graduates of West Point (Henry H. Jr., 1939; Willam Bruce, January 1943; and David Lee, 1949) and the two youngest are buried near their father's burial site at Arlington National Cemetery.

Henry "Hap" Arnold was also voted as the exemplar for the Class of 2012 at the United States Air Force Academy.