April 3 – The first handheld mobile phone call is made by Martin Cooper of Motorola in New York City. April 5 Fahri Korutürk becomes the sixth president of Turkey. Pioneer 11 is launched on a mission to study the Solar System. April 6 – Ron Blomberg of the New York Yankees becomes the first designated hitter in Major League Baseball. April 7 – Tu te reconnaîtras by Anne-Marie David (music by Claude Morgan, text by Vline Buggy) wins the Eurovision Song Contest 1973 for Luxembourg. April 10 – Operation Spring of Youth: Israeli commandos raid Beirut, assassinating 3 leaders of the Palestinian Resistance Movement. The Lebanese army's inaction brings the immediate resignation of Prime Minister Saeb Salam, a Sunni Muslim. April 10 – The Islamic Republic of Pakistan introduced its new constitution, its supreme law. April 15 – Naim Talu, a former civil servant, forms the new government of Turkey (36th government). April 17 – The German counter-terrorist force GSG 9 is officially formed in response to the Munich massacre. May May 3 – The Sears Tower in Chicago, United States, is topped-out, becoming the world's tallest building at . May 5 – Shambu Tamang becomes the youngest person to climb to the summit of Mount Everest. May 10 – The Polisario Front, a Sahrawi movement dedicated to the independence of Spanish Sahara, is formed. May 11 – The Data Act (Sw. Datalagen) − the world's first national data protection law − is enacted in Sweden. May 14 – Skylab, the United States' first space station, is launched. May 18 – Second Cod War: Joseph Godber, British Minister of Agriculture, Fisheries and Food, announces that Royal Navy frigates will protect British trawlers fishing in the disputed limit around Iceland. May 25 Skylab 2 (Pete Conrad, Paul Weitz, Joseph Kerwin) is launched on a mission to repair damage to the recently launched Skylab space station. Héctor José Cámpora becomes democratic president of the Argentine Republic ending the 1966 to 1973 Revolución Argentina military dictatorship. May 30 – Gordon Johncock wins the Indianapolis 500 in the Patrick Racing Special Eagle-Offenhauser, after only 133 laps, due to rain. (The race was begun May 28 but called due to rain.) June June 1 – The Greek military junta abolishes the monarchy and proclaims a republic. June 3 – A Tupolev Tu-144 crashes at the Paris air show; 15 are killed. June 10 –