January 26 – In the Spanish Civil War, Barcelona surrenders to Nationalist forces. In the days leading up to the surrender, Nationalist aircraft have raided the city continually, especially targeting ships in port to prevent them from saving Republican refugees from capture.
February 11 – The Lockheed XP-38 falls 17 minutes short of the record for a flight across the United States, flying from March Field, California, to Mitchell Field, New York, in 7 hours 43 minutes. It loses power and crashes during its final approach at Mitchell Field, but its pilot is unhurt and the flight is considered an impressive demonstration of range and speed for a fighter.
February 12 – Spanish Nationalist forces have 600 aircraft, compared to only 40 available on the Republican side.
March 25 – Ongoing ceasefire negotiations between Nationalist and Republican officials which include a Nationalist demand that all Spanish Republican Air Force aircraft fly to Nationalist airfields to surrender on this day are broken off when Republican aircraft do not surrender. A major motivation for the Nationalist demand is to prevent Republican leaders from fleeing Spain by air; six Republican aircraft carry officials and refugees from central Spain to France on this day.
March 26 – Republican leader Segismundo Casado López telegraphs Nationalist leader Francisco Franco, announcing that the Spanish Republican Air Force will surrender to Nationalist forces the following day. Franco replies that Nationalist armies would advance on Republican territory anyway.
April 1 – Nationalist leader Francisco Franco announces that the Spanish Civil War has ended in a complete Nationalist victory. During the 32½-month war, the Nationalists have used about 1,300 aircraft and the Republicans about 1,500; about 10,000 people have died in air attacks. Early Republican numerical air superiority had been challenged almost immediately by the technical superiority of Italian Fiat CR.32 fighters and Savoia-Marchetti SM.81, and German Junkers Ju 52 bomber-transports; Soviet Polikarpov I-15 and I-16 fighters had given the Republicans air superiority in the winter of 1936-1937, but the Nationalists had achieved lasting air superiority after German Messerschmitt Bf 109 fighters and Heinkel He 111 bombers and Italian Savoia-Marchetti SM.79 bombers had arrived in 1937. Germany has sent about 600 aircraft to Spain, Italy about 660, the Soviet Union 1,000, and other countries (principally France) about 350. The German, Italian, and Soviet air forces have learned a great deal about the employment of modern aircraft in warfare through their involvement, and the Luftwaffe's Condor Legion in particular has used the conflict to test new aircraft and revolutionary new air warfare concepts.
The Imperial Japanese Navy's air arm conducts the first Japanese bombing raid on Chungking, China, an incendiary raid which causes huge fires and inflicts enormous casualties. Raids will increase in size and intensity over the next two years.
May 24 – The Royal Navy takes practical control of British naval aircraft for the first time since the dissolution of the Royal Naval Air Service in 1918. British naval aircraft, since 1918 under Royal Air Force control and since 1924 known collectively as the "Fleet Air Arm of the Royal Air Force," officially become the Royal Navy's Air Branch, although the term "Fleet Air Arm" remains in widespread informal use and finally will be adopted officially in 1953.
May 26 – German personnel of the Condor Legion depart Spain.
May 31 – Italian forces, including the "legionary air force," depart Spain.
June 29 – During another Khalkhin Gol Incident dogfight between Soviet and Japanese aircraft, the Soviets claim to have shot down 25 Japanese planes in exchange for the loss of two Soviet aircraft.
Serving as a testbed for the Heinkel HeS 3turbojet with the jet engine slung under its fuselage, a Heinkel He 118dive bomber takes off and lands using its piston engine but flies under jet power after the turbojet is started in flight. It is the first time any aircraft makes any part of a flight under jet power, and the successful test leads to the first flight made completely under turbojet power by the Heinkel He 178 the following month .
August 26 – The Messerschmitt Me 209 V1 (registration D-INJR) sets a new world speed record of 755 km/h (469 mph), not officially broken by another piston-engined aircraft until 1969.
August 24 – The Royal Air Force forms the Advanced Air Striking Force. Initially consisting of 10 squadrons of Fairey Battle bombers, its mission is to deploy to France in the event of war with Germany and strike targets in Germany from French bases.
September 1 – The German Luftwaffe has 3,650 combat aircraft (1,170 bombers, 335 dive bombers, 1,125 single-engine fighters, 195 twin-engine fighters, 620 reconnaissance aircraft, and 205 coastal aircraft); a reserve force of between 10 and 25 percent of each of these types; and a training organization with 500 operational types used for operational training and 2,500 other training aircraft.
September 2 – By the end of the day, the Luftwaffe has achieved virtually complete air superiority over Poland. It switches over to support of German Army ground forces for thr rest of the Polish campaign, knocking out roads, railroads, and bridges – sometimes so effectively that the movement of Polish Army forces becomes impossible – and attacking Polish troop concentrations and destroying artillery and antiaircraft artillery units.
September 4 – The first British bombs of the war are dropped on German targets when a Bristol Blenheim of 110 Squadron attacks the German fleet. During the day, 30 Blenheims and Vickers Wellingtons attack the German ships, with seven of the bombers shot down. One of the Wellingtons mistakenly bombs Esbjerg in neutral Denmark, killing two people. They are the first civilians killed by Royal Air Force bombs in World War II.
September 15 – The Khalkhin Gol Incident concludes in a Soviet victory over the Imperial Japanese Army. In the final August 20-September 15 Soviet offensive, the Soviet Air Force claims the destruction of another 290 Japanese aircraft, bringing the total Soviet claim since the beginning of the Incident on May 11 to 645 Japanese planes destroyed. The Soviets claim to have lost only 34 aircraft in the last two months of the conflict.
September 25 – As Adolf Hitler looks on from a camouflaged bunker outside of the city, about 400 Luftwaffe bombers – some flying more than one sortie during the day – attack Warsaw, Poland, in conjunction with a German Army artillery bombardment, leaving the entire city ablaze. Its defenders surrender the next day.
October 6 – The Polish campaign ends as Germany and the Soviet Union gain effective control over all of Poland. During the campaign, the Luftwaffe has lost 285 aircraft – 79 fighters, 78 bombers, 31 dive bombers, and 97 other aircraft – destroyed; 279 aircraft damaged; and 413 aircrew killed and 126 wounded. Poland has lost 333 aircraft.