He attended St. John's College in Annapolis with the intention of entering West Point, but unable to secure an appointment, he followed his older brother into the Naval Academy in 1907, graduating in June 1911, ranked 58th in merit in a class of 194. In March 1911, he submitted a letter of resignation effective on the date of graduation, listing seasickness as a primary reason, and as a result, the Academy's Permanent Medical Examining Board rejected him for active duty.
In July 1916, he was promoted to first lieutenant and sent to the Philippines to join the 1st Company, Fort Mills (138th Company CAC) on Corregidor. Less than two months later he requested to return to the Aviation Section, Signal Corps. Because of the "Manchu Law" (widespread Army colloquialism for the Detached Service provision included in the Army's 1912 appropriations bill to underpin the regulation made in 1911) regulating length of detached service away from an officer's permanent branch, Brereton first transferred to the 17th Field Artillery Regiment to qualify, and was assigned to duty with the 2nd Aero Squadron, also stationed on Corregidor, on January 17, 1917. Returning to the United States in March 1917, he was assigned to duty in Washington, D.C., at the Aviation Section headquarters in the Office of the Chief Signal Officer.
After World War I began, Brereton entered flying training a second time at Hazelhurst Field, Mineola, New York. While in pilot training he was promoted to captain on May 15, 1917, and received a new rating of Junior Military Aviator on June 27. During most of the remainder of 1917, he worked in the Equipment Division at Aviation Section headquarters under Col. Benjamin D. Foulois. In November, when Foulois was promoted to brigadier general and sent to France to command the Air Service of the AEF, he took with him 100 members of his staff, including Brereton. Although initially sent to a Services of Supply unit, Brereton's JMA rating enabled him to enter advanced flying training at Issoudun, which qualified him to take command of the 12th Aero Squadron on March 1, 1918. His unit had no aircraft on his arrival, and he could only procure a dozen obsolete Dorand AR.Is to fly until first-line Salmson 2 A2s became available. The 12th A.S. began combat operations from Ourches airdrome on May 3, patrolling the "Toul Sector" between Flirey and Apremont in support of the U.S. 26th Division Brereton and his pilots moved overland to Vathiménil to receive their Salmsons in the first week of June and carried out extensive operations between Blâmont and Badonviller in the "Baccarat Sector" for three weeks supporting the U.S. 42nd Division.
Upon his returned to the United States in early 1919, he was assigned to the Office of the Director of Air Service, Major General Charles T. Menoher. When Menoher reorganized the office in March, under an executive order issued by President Woodrow Wilson, and established a "divisional system", Brereton was picked as Chief of the Operations Division, Training and Operations Group, again under Gen. Mitchell. He remained there until December 1919, when he became an assistant military attaché for air at the U.S. Embassy, Paris, France, under Ambassador Myron T. Herrick. Brereton served in Paris until August 1922, where he learned "to speak French with a Parisian accent", and to "appreciate fine wine". On July 1, 1920, the Air Service was given statutory existence as a combatant arm of the line, and Brereton became a member in the permanent rank of major, a rank he held for the next 15 years.
Brereton became commanding officer of the 10th School Group on September 1, 1922 at Kelly Field, Texas, responsible for the advanced flying training of pilot candidates. At Kelly, Brereton successively became Assistant Commandant of the Advanced Flying Training School, Director of Attack Training, and President of the Board of Attack Aviation. On February 5, 1923, while on an inspection tour, Gen. Mitchell relieved the inexperienced commander of the 3rd Attack Group, at that time one of only three combat groups in the Air Service, and replaced him with Brereton. During this period the 3rd Attack Group conducted field tests on the new Boeing GA-1, a heavily armed and armored attack aircraft, ultimately determining it to be unfit for combat service. On September 16, 1924 he transferred to Langley Field as an instructor at the Air Service Tactical School for its 1924-1925 term.
Between July 7, 1931 and June 20, 1935, Brereton served in the Panama Canal Zone. He concurrently commanded the 6th Composite Group, France Field, and the Panama Air Depot. His superior in Panama was the same Gen. Brown who had rejected him for duty at First Corps Area headquarters, but Brereton's work performance reversed the general's earlier opinions and he received excellent ratings that restored the professional reputation nearly destroyed in 1927. On March 4, 1935, he received promotion to lieutenant colonel and became Air Officer, Panama Canal Department.
Shortly after word of the attack on Pearl Harbor reached the Philippines on December 8, 1941, Brereton urged immediate air attacks against Japanese bases on Formosa in accordance with the Rainbow 5 war plan and Brereton's own aggressive nature. However, Brereton was twice thwarted by General Douglas MacArthur's chief of staff from seeing him about an attack, and sent his bombers and P-40 pursuit planes aloft to prevent them from being destroyed by air attack. Hours later, MacArthur initially denied permission for the attack, but then reversed himself minutes afterwards. Brereton ordered his bombers to return to base to prepare for the mission, and by then all fighters aloft had become short on fuel. While they were being fueled and armed for the afternoon mission, the bombers and many of the pursuit planes were caught on the ground when Japanese air units, whose takeoff from Formosa had been delayed for six hours by fog, attacked shortly after noon. Consequently, FEAF was largely destroyed on the first day of the war.
In early 1942, Brereton was named Deputy Air Commander, under Royal Air Force Air Marshal Sir Richard Peirse, of ABDAIR, a component of the short-lived ABDACOM unified command of Allied forces in Southeast Asia and the Southwest Pacific. He also resumed active command of FEAF. Brereton arrived on Java on January 10, 1942, and except for a nine-day period at the end of January when he acted as commander of United States Army Forces In Australia, remained until February 23, despite requesting relief from command on February 8 over "honest differences" with Peirse and demoralizing criticism from the British commander of ABDACOM, Gen. Sir Archibald Wavell. Brereton received a cable from Gen. George C. Marshall on February 22 giving him complete freedom of action in evacuating himself and his headquarters from Java, including destination, and he left for India via Ceylon on February 24 before orders from Arnold to organize an air force in Australia could reach him. For his performance in commanding the FEAF, Brereton received his first award of the Distinguished Service Medal on February 18, 1943.
On March 5, 1942, in New Delhi, Brereton took command of and began to organize the new Tenth Air Force. In addition to setting up the new air force, Brereton was also ordered to prepare an air route for the resupply of China. On the night of April 2–3, 1942, he participated in the first bombing mission of the Tenth Air Force—an LB-30 and two B-17s, of which he co-piloted one of the latter—in an attack against Japanese warships at Port Blair in the Andaman Islands in support of the British, for which he was decorated with the Distinguished Flying Cross.
n June 1942, Brereton was appointed commander of United States Army Middle East Air Forces. He formed a provisional bomb group from 19 Consolidated B-24 Liberators of the Halverson Detachment and the nine B-17s he had brought from India. It was forced to fall back to Lydda in Palestine. With the arrival of B-24s of the 98th Bomb Group at the end of July 1942, USAMEAF began to attack depots in Libya, the chief of which was Tobruk, and ship convoys as far away as Navarino Bay in Greece.
In January 1943, the Combined Bomber Offensive plan was approved by the Combined Chiefs of Staff, calling for a force of 2,700 heavy bombers and 800 medium bombers, based in England, to attack German targets on the continent around the clock. In April, Maj. Gen. Ira C. Eaker, commanding the Eighth Air Force, submitted a plan to the USAAF requesting creation of a new tactical air force within the Eighth AF of 25 medium and light bomb groups to carry out the medium bomber portion of the CBO plan. His proposal was investigated and endorsed by a committee from Headquarters USAAF under Brig. Gen. Follett Bradley. At the same time but unrelated to the CBO, Gen. Dwight D. Eisenhower proposed a consolidation of the Ninth and Twelfth Air Forces, and suggested that Brereton be re-assigned as deputy commander of the Allied tactical air force commanded by Air Marshal Arthur Coningham.
During the winter of 1943–44 Ninth Air Force expanded at an extraordinary rate. In six months under Brereton's command, October 16, 1943 to April 16, 1944, the Ninth Air Force expanded from 2,162 to 163,312 men. By the end of May, its complement ran to 45 flying groups operating 5,000 aircraft. Organizationally it had added an Engineer Command, an Air Defense Command, and two Air Support Commands, which were redesignated Tactical Air Commands (TAC) on April 18, 1944, and by D-Day had received and trained 11 medium bomb groups, 19 fighter groups, 14 troop carrier groups, and a photo-reconnaissance group. The total number of personnel assigned to Ninth Air Force was more than 200,000, a total greater than that of the Eighth Air Force.
Brereton was promoted to lieutenant general in April 1944 as his units began a campaign of planned attacks against airfields (April 1), railway centers and rolling stock (April 1), coastal batteries (April 13), and bridges (May 7) in France preparatory to Operation Overlord, the invasion of Normandy by the Western Allies on June 6, 1944.
Physical Characteristics: He was physically described early in World War II as "5-06", "stocky build", "brown-eyed", "black-haired", and "raspy-voiced". His personality characteristics were said to be "cool and thoughtful", able to "think rapidly on his feet", with a "quick, analytical mind". However, he was also said to have an "appropriate temper" and "able to swear in three or four languages", a "party-loving streak", and when referring to himself, to use the third person. He had a reputation, especially among critics, for being hedonistic. Gen. Omar N. Bradley, who intensely disliked Brereton, was quoted by a biographer of Dwight D. Eisenhower as saying that Brereton was "marginally competent...(and) more interested in living in the biggest French chateau".
He met and married Helen Willis while stationed in San Diego, and subsequently had two children.