Before dawn, Germany invades Yugoslavia from Austria, Romania & Bulgaria, while Italian troops cross the border from Albania and Italy. Yugoslavia will be crushed from all sides in a classic blitzkrieg. Luftwaffe destroys most Yugoslav aircraft on the ground and bombs the capital Belgrade from 7-8.30 AM, killing 4,000 civilians. German armoured columns from Bulgaria bypass antiquated Yugoslav mountain defenses and rush down the river valleys almost 100 miles towards Greece, reaching Skopje and Veles in Southern Yugoslavia. Simultaneously, German mountain troops invade Greece from Bulgaria but they are quickly held at the Metaxas Line. 2 forts in the Metaxas Line are destroyed by German bombing. Overnight, Luftwaffe bombs Greek port of Piraeus setting on fire British munitions ship SS Clan Fraser (cargo of TNT explodes destroying the harbour and sinking 11 other freighters).
Libya. British and Australians withdraw in panic from Barce and Derna towards Tobruk, as German advances through the desert South of Green Mountain threaten to cut off their retreat along the coast. By 5 PM, Germans surround British forces at the old desert fort at Mechili but British Brigadier Vaughn refuses German demands for surrender. British commanders, General Neame and General O’Connor, pick a bad day to visit the front. They get lost in the retreat and are captured overnight between Mechili and Derna.
11th African Division advances 120 miles in 2 days to reach the Ethiopian capital Addis Ababa, but find it unoccupied. The Italians have withdrawn North to mountain strongholds of Gondar and Amba Alagi. General Cunningham's African force has advanced 1,725 miles from Kenya in 72 days, capturing 22,000 Italian and colonial prisoners.
British armed merchant cruiser HMS Comorin carrying military personnel to Freetown, Sierra Leone, catches fire 450 miles West of Ireland (20 dead). Despite very heavy seas, 405 men are taken off by British SS Glenartney and destroyers HMS Broke & HMS Lincoln (which sinks the wreck next day by shellfire).
German battlecruiser Gneisenau, waiting to have an unexploded bomb removed before entering dry dock at Brest, France, is attacked by RAF bombers and badly damaged with a torpedo.
At 5 PM 100 miles Southwest of Iceland, U-94 sinks Norwegian tanker Lincoln Ellsworth with 2 torpedoes and 121 rounds from the deck gun. All 29 crew abandon ship in 2 lifeboats and are picked up after 2 days by armed merchant cruiser HMS Derbyshire and Icelandic fishing boats.