Yugoslavia officially surrenders after just 12 days. In Belgrade, Yugoslav Foreign Minister Cincar-Marcovic signs an armistice with Germany and Italy. The Hungarians, technically "not at war with Yugoslavia", do not sign the armistice. Germans capture 2 Yugoslav destroyers Beograd and Dubrovnik at the Adriatic port of Kotor, but destroyer Zagreb is scuttled by her crew (2 killed).
In Greece, New Zealand 21st battalion reinforced by Australian 2/2nd Battalion demolish the Pinios River railway bridge and hold the Tempe and Pinios Gorges, delaying the German advance down the Aegean coast. This allows Allied troops to withdraw to new defenses on the Thermopylae line.
Iraq’s new National Defense Government led by Rashid Ali al-Gaylani, which seized power in a coup d’etat on April 1, requests German military assistance to eject the British from Iraq. Rashid Ali has already sent an artillery force to surround the RAF airbase at Habbaniya. British garrison is reinforced with 1st Battalion King's Own Royal Regiment which is flown from Karachi, India, to another airbase RAF Shaibah near Basra.
Tobruk, Libya. Italian infantry and tanks attack in early afternoon. Again, the attack is broken up by British artillery fire but 6 tanks break through the wire, crossing an Allied minefield which fails to detonate. 7 British cruiser tanks engage the tanks while Australian troops again trap the following infantry in crossfire. Only 1 Italian tank escapes back through the wire. After dark, there is a running tank exchange across the perimeter wire (3 of 12 Axis tanks destroyed). Rommel, running low on ammunition and other supplies, decides to wait until 15th Panzer Division arrives in strength before making a concerted attack on Tobruk. Off Libyan coast, British submarine HMS Truant sinks Italian barque Vanna carrying ammunition and fuel to Derna.
At 5.30 PM 600 miles West of Ireland, U-123 sinks Swedish MV Venezuela (the crew of 49 abandon ship in lifeboats but are never found).
German motor torpedo boats S.41 S.42 S.43 S.55 and S.104 attack Convoy FS464 off Great Yarmouth, England, sinking 2 small freighters and damaging a large steamer. The German S-boats are engaged by British motor gun boats MGB.60, MGB.59, and MGB.64, without success.