and Stjepan Burazović, Colonel General Miodrag Lazić, Milorad Petrović and many other general officers (with British support) forces Prince Paul into exile; 17-year-old King Peter II assumes power following the coup and Simović is elected new Prime Minister of Yugoslavia. Japanese spy Takeo Yoshikawa arrives in Honolulu to study the United States Pacific Fleet at Pearl Harbor, in preparation for a future attack. March 30 – WWII: All German, Italian and Danish ships anchored in United States waters are taken into "protective custody". A German Lorenz cipher machine operator sends a 4,000-character message twice, allowing British mathematician Bill Tutte to decipher the machine's coding mechanism. April April – The Valley of Geysers is discovered on the Kamchatka Peninsula of Russia, by Tatyana Ustinova. April 1 – A military coup d'état, launched by Rashid Ali Al-Gaylani, overthrows the pro-British regime in Iraq. April 4 – WWII: Axis forces capture Benghazi. April 6 – WWII: Germany invades Yugoslavia and the Battle of Greece begins. April 9 – The U.S. acquires full military defense rights in Greenland. April 10 – WWII: U.S. destroyer , while picking up survivors from a sunken Dutch freighter, drops depth charges on a German U-boat (the first "shot in anger" fired by America against Germany). The Independent State of Croatia, a puppet state of the Axis powers, is established with Ustashe leader Ante Pavelić as head (Poglavnik) of the government. April 12 – WWII: German troops enter Belgrade. April 13 – The Soviet–Japanese Neutrality Pact is signed. April 15 – WWII: Axis forces reach Halfaya Pass, on the Libyan-Egyptian frontier. April 18 – WWII: The Yugoslav Royal Army capitulates. Greek Prime Minister Alexandros Koryzis commits suicide as German troops approach Athens. April 19 – Bertolt Brecht's anti-war play Mother Courage and Her Children () receives its first theatrical production, at the Schauspielhaus Zürich. April 21 – WWII: Greece capitulates to Germany. Commonwealth troops and some elements of the Greek Army withdraw to Crete. April 23 – The America First Committee holds its first mass rally in New York City, with Charles Lindbergh as keynote speaker. April 25 – Franklin D. Roosevelt, at his regular press conference, criticizes Charles Lindbergh by comparing him to the Copperheads of the Civil War period. In response, Lindbergh resigns his commission in the U.S. Army Air Corps Reserve on April 28. April 27 – WWII: German troops enter Athens. April 28 – World