1-18 April
Politics, Iraq
Nationalist politician Rashid Ali and army officers hostile to Britain depose Regent Faisal and form a pro-Axis regime in Iraq. British troops begin arriving in Iraq on the 18th to safeguard access to key oil supplies.
4 April
Africa, Libya
General Erwin Rommel’s Axis troops are advancing across Libya in three groups. A predominantly Italian force on the coast takes Benghazi. Another group inland is advancing to Msus, while farther south a third force is also heading toward the same objective.
6-15 April
Balkans, Yugoslavia/Greece
Thirty-three German divisions, with Italian and Hungarian support, invade Yugoslavia from the north, east, and southeast. Aerial bombing centering on Belgrade dislocates the nation’s military command and communication structure, and further undermines the ineffective mobilization of its 640,000-strong army. Major cities are quickly seized, including Zagreb, Belgrade, and Sarajevo, between the 10th and 15th.
In Greece, German forces attack the Greek Second Army on the fortified Metaxas Line along the country’s northern border with Bulgaria. Air raids on Piraeus port destroy a British ammunition ship, which explodes and sinks 13 vessels. The Second Army, cut off after German forces reach the sea at Salonika on the 9th, soon surrenders. The British, after initially occupying positions between Mount Olympus and Salonika, are quickly forced back to a new defensive line just north of the mountain following the collapse of Greek forces on their left flank.
6-9 April
Africa, Ethiopia/Eritrea
British General Sir Alan Cunningham, after an impressive advance of over 1000 miles (1600 km) from Kenya, captures Addis Ababa, Ethiopia’s capital, and then continues to harass the retreating Italian forces. Allied forces in Eritrea then seize the port of Massawa on the 9th and capture 17 Axis merchant vessels and other assorted craft in the harbor.
7 April
Africa, Libya
General Erwin Rommel captures Derna, along with British Generals Philip Neame and Sir Richard O’Connor, during his advance toward Tobruk.
10 April
Politics, Yugoslavia
The Ustachi political group in the province of Croatia declares the formation of an independent republic separate from Yugoslavia.
Sea War, Greenland
The United States begins occupying Greenland to prevent the Danish colony falling into German hands. Valuable weather-observation points for Britain are situated in Greenland.
10-13 April
Africa, Libya
General Erwin Rommel begins the siege of Tobruk. The Allies, who repulse his first attacks, are determined to hold Tobruk as it is the only major port between Sfax in Tunisia and Alexandria in Egypt, a distance of 1000 miles (1600 km). It is therefore a strategic base for forces fighting in North Africa. Tobruk comes under constant air and ground attack, its caves providing the only real shelter, while the sea-lane to Egypt is to be its only lifeline.
13 April
Politics, Soviet Union/Japan
A five-year nonaggression pact between the Soviet Union and Japan is signed, which enables the Red Army to move units from Siberia to bolster its forces preparing to meet any future German attack.
17 April
Politics, Yugoslavia
Yugoslavia signs an armistice with Germany. The country is now under military administration except for the Croatian puppet state. Immediately, guerrilla forces emerge to resist the Nazi occupation.
18-21 April
Balkans, Greece
Greek positions are quickly collapsing as the German invaders advance. The British have fallen back from Mount Olympus to Thermopylae. A British evacuation appears inevitable as reinforcements from Egypt are canceled on the18th. King George assumes temporary charge of the government after the premier, Alexander Koryzis, commits suicide. A British evacuation is finalized after General Alexander Papagos, the Greek commander-in-chief, realizing the situation is hopeless, recommends a withdrawal on the 21st. Greek forces fighting in Albania surrender on the 20th.
21-30 April
Air War, Britain
Two raids on the nights of the 21st-22nd and 29th-30th against Plymouth by 640 bombers claim 750 lives and leave 30,000 homeless.
21-27 April
Balkans, Greece
British forces leave their lines around Thermopylae on the 24th after Greek forces in Thrace capitulate. The British evacuation operation now begins, and some 43,000 men are rescued by the Royal Navy from ports and beaches in Eastern Greece, while under constant German air attack. Two destroyers and four transport ships are lost.
A German attack by paratroopers at Corinth on the 26th and an advance to Patras pose a threat to the British evacuation. German forces occupy Athens on the 27th, but the Greek government has already left for Crete. Campaign dead: Greek 15,700; Italian 13,755; German 1518; and British 900.
25 April
Politics, Germany
Adolf Hitler issues Directive No. 28, ordering the airborne invasion of Crete, code-named Operation Mercury.
30 April
Africa, Libya
The most intense Axis attack on Tobruk to date commences but meets determined resistance from the defenders. Four days later Axis forces secure a salient on the southwestern area of the defensive peri-meter. Both sides then dig in for a lengthy campaign, with the garrison entirely dependent on supplies carried by the Royal Navy. German submarines, torpedo-boats, and medium and dive-bombers constantly threaten the supply vessels, which are especially vulnerable when unloading.