1940 in aviation

January
January 6 - During the Winter War between the Soviet Union and Finland, Finnish Lieutenant Jorma Sarvanto managed to shoot down six Soviet Tupolev DB-3 bombers in one mission.

March
March 16 - The United Kingdom suffers its first civilian air-raid casualties of the war after a raid by KG 26 on Scapa Flow

March 25 - the U.S. government grants permission to the country's aircraft manufacturers to sell advanced combat aircraft to nations fighting the Axis powers.

April
April 9 - Germany invades Denmark and Norway, making extensive use of paratroops

April 13 - The British Royal Air Force (RAF) begins deploying sea mines around Germany's coastal waters.

April 24-28 - aircraft carrier HMS Glorious evacuates the Gloster Gladiators of No. 263 Squadron RAF from Norway

May
May 10 - Germany invades the Netherlands, Belgium, and Luxembourg. Paratroops again play a key role.

May 13 - the Sikorsky VS-300, which made its first flight the previous year, makes its first untethered flight.

May 15-16 - British bombers make their first attack on German land targets, in the Ruhr Valley

June
June 4 - BOAC commences a twice-weekly service between the United Kingdom and Portugal, scheduled to connect with Pan Am flights from Lisbon to New York.

June 8 - after a second expedition to Norway, HMS Glorious is sunk by German battlecruisers (or light battleships) Scharnhorst and Gneisenau.

June 10 - Italy declares war on the United Kingdom and France. The Italian Royal Air Force (Regia Aeronautica), the Italian Royal Navy (Regia Marina), the German Air Force (Luftwaffe), and the German Navy (Kriegsmarine) begin the "Siege of Malta".

July
July 10 - the Battle of Britain commences with the first German attacks on British convoys in the English Channel.

August
August 15 - the heaviest fighting of the Battle of Britain occurs, with the loss of 46 British and 76 German aircraft.

August 25-26 - The Royal Air Force makes its first air raid on Berlin of the war.

August 31 - Polish 303 Squadron, the most efficient allied unit of the Battle of Britain, enters action.

September
September 7 - Hermann Göring orders the German Air Force (Luftwaffe) to stop targeting British airfields and to attack the city of London instead.

September 7-September 8 - the largest mass air combat in history takes place over Great Britain, with 1,200 British and German aircraft operating in an area of only 24 x 48 km (15 x 30 miles).

September 15 - Germany makes its heaviest daylight raid on London

September 30 - The Battle of Britain is said to be over, with Hitler's planned invasion of the United Kingdom (Operation Sealion, or Unternehmen Seelöwe) postponed indefinitely.

October
October 8 - No. 71 Squadron RAF, "Eagle Squadron" is formed, comprising American volunteers.
October 8 - Josef František, the Czech ace (17 victories) - the most efficient allied pilot of the Battle of Britain, died in an aircrash.

November
November 5 - Four RAF squadrons are deployed to Greece to support the country against Italian attacks.

November 11 - Regular ferry flights of US-built warplanes commence across the Atlantic.

November 11-12 - Fairey Swordfish from HMS Illustrious make a highly successful raid against ships of the Italian Royal Navy (Regia Marina) at Taranto. The raid damaged the Italian battleship Conte di Cavour beyond repair, and extensively damaged two others, Littorio and Caio Duilio (see Battle of Taranto).

November 14-15 - 437 aircraft of the German Air Force (Luftwaffe) make a massed air raid on Coventry. 380 civilians were killed and some 800 were wounded.

December
December 23 - Eddie August Schneider dies in crash when his plane is clipped by a navy bomber at Floyd Bennett Field.

December 29-30 - the Luftwaffe makes a devastating attack on London, making extensive use of incendiary weapons.

First flights

Ikarus Aero 2

January
January 4 - Fairey Fulmar production aircraft N1854
January 13 - Yakovlev Ya-26, prototype of the Yakovlev Yak-1

February
February 24 - Hawker Typhoon prototype P5212

March
March 20 - Armstrong Whitworth Albemarle prototype P1361

May
May 18 - SAAB B17
May 29 - Vought XF4U-1

August
August 28 - Caproni-Campini N.1, thermojet-powered aircraft

September
September 7 - Blohm & Voss BV 222
September 14 - Miles M.20

October
October 12 - Ilyushin TsKB-57, prototype of the Ilyushin Il-2
October 18 - Airspeed Fleet Shadower
October 26 - North American NA-73X, prototype of the P-51 Mustang

November
November 25 - de Havilland Mosquito prototype W4050
November 29 - Junkers Ju 288

December
December 7 - Fairey Barracuda prototype P1767
December 18 - Curtiss SB2C Helldiver

Entered service

February
Blackburn Roc

March
Fairey Albacore with No. 826 Squadron FAA

May
Dewoitine D.520 with French squadrons

July
Fairey Fulmar with No. 806 Squadron FAA
Westland Whirlwind with No. 263 Squadron RAF

November
Avro Manchester with No. 207 Squadron RAF

November 23 - Handley Page Halifax with No. 35 Squadron RAF