SIGSALY, the X System vocoder "Green Hornet", went into operation for use in secure phone conversations between American President Franklin D. Roosevelt & British Prime Minister Winston Churchill. This new system, developed by AT&T's Bell Labs, encrypted speech into electronic signals that could be transmitted at the rate of 1,551 bits per second, and decrypted at the other end, permitting the two wartime leaders to talk to each other without being understood by wiretappers. The terminals for transatlantic calls were at the Pentagon in Washington DC and the basement of Selfridges department store in London.

Bolivia declares war on Germany, Japan and Italy

Allied Bomber Offensive: Heavy night-time British air raid, 100+ aircraft attack on St-Nazaire & Lorient, France. Last attack on these targets. Both targets were largely deserted by the civilian population at this time

King Boris III of Bulgaria told German Foreign Minister Joachim von Ribbentrop that the 25,000 Jews in Bulgaria would not be turned over to German control, despite the alliance between the two Axis powers. At most, the King said, the Bulgarian government might intern its Jewish citizens in camps under Bulgarian control.

Allied Bomber Offensive: Heavy night-time British air raid, 350+ aircraft attack on Essen, Germany. Successful raid widespread destruction of the target.

The Battle of Manners Street, a riot in Wellington, New Zealand, between American servicemen and New Zealand servicemen and civilians, occurred when some of the American servicemen refused to allow Māori soldiers to enter the Allied Services Club. Dozens of people were injured but news of the riot was censored at the time.

Shipwrecked steward Poon Lim was rescued by Brazilian fishermen after being adrift for 131 days as the sole survivor of a British merchant ship, the SS Benlomond, which had been torpedoed on November 29, 1942.

Allied Bomber Offensive: Heavy night-time British air raid, 570+ aircraft attack on Kiel, Germany. Unsuccessful raid because of poor weather & marking.

American B-24 bomber 'Lady Be Good' became lost over the North African desert after completing a bombing raid in Italy, ran out of gas, and crashed after its crew parachuted to safety. The nine-member crew died of thirst, one by one, over the next eight days. For nearly 16 years, Lady Be Good would remain missing until its discovery on 27th February 1959. The bodies of the men would be found almost a year after that, on 11th February 1960.

German radio announced that three former imprisoned leaders of the French Government Prime Ministers Édouard Daladier & Léon Blum, along with the former French Army commander-in-chief, General Maurice Gamelin, have been handed over to the Germans by the Vichy French. They had been held in custody in France since the 1940 surrender. This was done to stop the "establishment of a counter-government". They would be sent to Buchenwald concentration camp until the end of the war.

Allied Bomber Offensive: Large day-time American air raid, 210+ aircraft attack on Mortsel, Belgium. Poor results

Lutheran pastor Dietrich Bonhoeffer was arrested at the headquarters of the German military intelligence (the Abwehr) by the Nazi secret police (the Gestapo) along with lawyer Hans von Dohnanyi, and both were found to have incriminating materials in their possession, showing cooperation with the enemy in Britain.

Five members of the U.S. Army Air Forces were rescued after having been marooned on an icecap in Greenland for almost five months. The men had been on a B-17 bomber that made a crash landing while searching for another lost plane but was kept alive with supplies dropped by Colonel Bernt Balchen, an Arctic explorer and aviator.

A four-day meeting between Adolf Hitler & Benito Mussolini at the Schloss Klessheim near Salzburg. Mussolini was in poor health and would spend most of the conference listening silently to Hitler's long rambling monologues; an attempt by Mussolini to bring up the possibility of making peace with the Soviets was swiftly rebuffed.

The British government published a plan drawn up by John Maynard Keynes for a postwar economy. The plan proposed an international monetary fund which could help any nation out of temporary financial difficulties. In return, that country would have to adopt policies aimed at restoring stability.

North African Campaign: The Battle of Wadi Akarit, Tunisia also known as Operation Scipo ended in Allied victory.

Allied Bomber Offensive: Heavy night-time British air raid, 390+ aircraft attack on Duisburg, Germany. Mixed results moderate damage.

The Japanese decided to use forced labour (Allied POWs) to build a new railway in northern Burma.

Liquidation of the Jews in the Zborow ghetto in German-occupied Ukraine began, with the shooting of about 2,300 people on the first day.

Allied Bomber Offensive: Heavy night-time British air raid, 390+ aircraft attack on Frankfurt, Germany. Mixed results moderate damage.

North African Campaign: The Tunisian port of Sfax was captured by British forces. Sfax was part to be the main port for the planned invasion Allied invasion of Sicily.

Martin Bormann was appointed as Secretary to the Führer, the second highest office in Nazi Germany.

On Budget Day in the United Kingdom, Chancellor of the Exchequer Sir Kingsley Wood announced that the war had cost Britain a total of £13 billion to date and was costing £15 million per day. In the new financial year, excess expenditure over revenue was estimated at £2,848,614,000.

The British War Office made its first report on the intelligence gathered concerning Germany's missile program, V-2, with the title "German Long-Range Rocket Development".

Katyn Massacre: German Government announce the discovery of mass graves in the Katyn forest. Soviet forces were blamed for the deaths of 10,000 Polish POWs.

Katyn Massacre: German Government announce the discovery of mass graves of Polish POWs in the Katyn forest. Soviet forces were blamed for these murders.

Allied Bomber Offensive: Heavy night-time British air raid, 200+ aircraft attack on La Spezia, Italy. Mixed results moderate damage. A handful of damaged aircraft flew onto Allied airfields in North Africa

The Commander of the 8th Japanese fleet broadcast a coded message concerning a tour of the fleet by the Naval Commander Admiral Isoroku Yamamoto beginning on the 18th of April. The itinerary of the tour was communicated via Japanese high-security code JN25 which Allied cryptanalysts had already broken.

Allied Bomber Offensive: Heavy night-time British air raid, 460+ aircraft attack on Stuttgart, Germany. Mixed results moderate damage.

North African Campaign: The Battle of the Cigno Convoy

Allied Bomber Offensive: Heavy night-time British air raid, 320+ aircraft attack on Pilzen, Czechoslovakia. Skoda factory was the target, but not hit during the raid.

Allied Bomber Offensive: Heavy night-time British air raid, 270+ aircraft attack on Mannheim, Germany. Successful attack. War production was stopped or reduced at 40 industrial premises.

The United States War Manpower Commission issued an order that prevented 27,000,000 civilian employees from changing jobs. An employee in an "essential activity" could not be hired for a job that was not essential to the war effort, unless he or she remained unemployed for at least 30 days. Likewise, a vital employer could not offer a higher wage rate to lure a worker from another vital employer without 30 days between jobs. Business owners and employees who violated the regulation were subject to a fine of up to $1,000 per violation and a year in prison. The manpower "freeze" was to remain in effect until the end of the war.

At a meeting in Salzburg with German Führer Adolf Hitler & Foreign Minister Ribbentrop, Admiral Miklós Horthy, the Regent and Head of State for the Kingdom of Hungary. Horthy refused a personal request by Germany to deliver 800,000 Hungarian Jews to the Nazis, despite the alliance between the two as Axis powers.

Japanese Admiral Isoroku Yamamoto, the Commander-in-Chief of the Japanese Navy and the architect of the December 7, 1941, attack on Pearl Harbor, is killed when the plane that he was on was shot down by American aircraft after American naval intelligence had intercepted and decoded a Japanese message that included the itinerary of his tour of the Solomon Islands. The body of Yamamoto, who was mortally wounded on Bougainville Island, was found the next day by a Japanese search party.

Allied Bomber Offensive: Heavy night-time British air raid, 170+ aircraft attack on La Spezia, Italy. Main railway station & public buildings hit.

Fourteen Germans of the White Rose anti-Nazi resistance group are found guilty and promptly executed for crimes against the Nazi regime.

British Prime Minster Winston Churchill announced in the House of Commons that restrictions on the ringing of church bells throughout Britain would be lifted now that the threat of German invasion had passed.

The escape of 233 Belgian Jews from a train bound for Auschwitz was made possible by a raid by three members of the Belgian resistance movement. The train was halted shortly after it had departed the concentration camp at Mechelen with 1,631 internees, bound for the Auschwitz concentration camp. Of the 233 who fled, 118 were able to get away. Another 89 were recaptured, and 26 were killed.

Allied Bomber Offensive: Heavy night-time British air raid, 340+ aircraft attack on Stettin, Germany. Successful attack from 600 miles away from the UK. Oboe used, the city found & 100 acres of the city centre destroyed.

Allied Bomber Offensive: Large night-time British air raid, 80+ aircraft attack on Rostock, Germany. Heinkel factory was the target, but a smoke screen concealed the target.

North African Campaign: The final Allied attack on Tunisia began with the opening of the Battle of Longstop Hill.

Allied Bomber Offensive: Heavy night-time British air raid, 560+ aircraft attack on Duisburg, Germany. Most targets in the city were missed.

North African Campaign: The Battle of Hill 609 began between American and German forces in Tunisia.

Allied Bomber Offensive: Large night-time British air raid, 160+ aircraft attack on ports of the Biscay & Brittany ports. Mine laying operation.

Allied Bomber Offensive: Large night-time British air raid, 200+ aircraft attack on ports off Heligoland, River Elbe, the Great Belts & Little Belts.

Allied Bomber Offensive: Heavy night-time British air raid, 300+ aircraft attack on Essen, Germany. Poor results.

The British submarine Seraph surfaced off of the coast of Spain, near Huelva, and dumped the body of "Major Martin" into the Mediterranean Sea as part of the Operation Mincemeat, to deceive German intelligence on plans for an Allied invasion of the continent. The body of "Major Martin" was found at around 9:30 am on 30 April 1943 by a local Spanish fisherman & taken to Huelva. Haselden, as vice-consul, was officially informed by the Spaniards; he reported back to the Admiralty that the body and briefcase had been found. A series of pre-scripted diplomatic cables were sent between Haselden and his superiors, which continued for several days. The British knew that these were being intercepted and, although they were encrypted, the Germans had broken the code; the messages played out the story that it was imperative that Haselden retrieve the briefcase because it was important.