Italians abandon the stalled invasion of Northern Greece and begin the retreat from the Kalamas River in Epirus. In the Pindus Mountains, remaining elements of the Italian Julia Division do not get the message but retreat anyway after learning of the coming Greek offensive from radio broadcasts from London.
Gabon,West Africa. Late in the evening, Free French forces (French Legionnaires plus colonial troops from Senegal and Cameroon) under General Marie Pierre Koenig land North and South of the capital Libreville and meet stiff resistance from defenders loyal to the Vichy regime. Libreville is also pressed inland by Free French troops from Cameroon.
Operation Crack. Aircraft from British carrier HMS Ark Royal, escorted by cruisers HMS Berwick and HMS Glasgow, attack the Italian seaplane base at Elmas near Cagliari, Sardinia. This is part of complex movements of several convoys with warship escorts through the Mediterranean (Operation MB8), including troops and anti-aircraft guns for Malta. The raid is also designed to distract from the planned attack on the Italian naval base at Taranto (Operation Judgement).
British WWI-era tug HMS Muria hits a mine and sinks off Isle of Thanet, just North of Dover, England (all hands lost). German bombers attack a convoy in the Thames Estuary, sinking or damaging several merchant ships. Convoy escort destroyer HMS Winchester shoots down 2 Ju87 dive bombers. HMS Winchester then hits a mine and, while anchored to make emergency repairs, she is bombed again and damaged by near misses (under repair in London until June 6 1941).
300 miles West of Ireland, Swedish steamer Vingaland is damaged by German bombers. Dutch submarine O-22 disappears in the North Sea 40 miles Southwest of the Norway, either lost on a mine or sunk by German submarine chasers UJ.117 and UJ.1102 (Dutch crew of 42 and 3 British sailors are lost). http://www.dutchsubmarines.com/boats/boat_o22.htm