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1911 (MCMXI)was a common year starting on Sunday of the Gregorian calendar and a common year starting on Saturday of the Julian calendar, the 1911th year of the Common Era (CE) and Anno Domini (AD) designations, the 911th year of the 2nd millennium, the 11th year of the 20th century, and the 2nd year of the 1910s decade. As of the start of 1911, the Gregorian calendar was 13 days ahead of the Julian calendar, which remained in localized use until 1923.
A highlight was the race for the South Pole.
- February 5
- The Missouri State Capitol building in Jefferson City, Missouri is destroyed by fire, after a bolt of lightning strikes the dome.
- The revolution in Haiti is suppressed after the leader, General Montreuil Guillaume, is captured by government troops and shot. General Millionard is executed two days later.
- February 11 – The Lincoln Memorial Commission is established, to find an ideal site for the proposed Lincoln Memorial.
- February 13 – HNK Hajduk Split, a Croatian football club, is founded.
- February 17 – The first "quasi-official" airmail flight occurs, when Fred Wiseman carries three letters between Petaluma and Santa Rosa, California.
- February 18 – The first official air mail flight, second overall, takes place from Allahabad, India to Naini, India, when Henri Pequet carries 6,500 letters a distance of 13 km.
- April 3 – Jean Sibelius conducts the première of his Symphony No. 4, in Helsinki.
- April 8 – Heike Kamerlingh Onnes discovers superconductivity; he presents his findings on April 28.
- April 13 – Mexican Revolution: Rebels take Agua Prieta on the Sonora–Arizona border; government troops take the town back April 17, when the rebel leader "Red" López gets drunk.
- April 18 – SS Lusitania, a 5,557-ton Portuguese passenger liner en route from Mozambique to Lisbon, strikes Bellows Rock just off Cape Point and sinks.
- April 19 – Mexican Revolution: Francisco I. Madero's troops besiege Ciudad Juárez, but General Juan J. Navarro refuses his surrender demand.
- April 22 – A passenger train from Port Alfred to Grahamstown, South Africa derails on the Blaauwkrantz Bridge, and plunges into the ravine 200 feet (61 metres) below, killing 31 and seriously injuring 23.
- April 26 – HŠK Građanski Zagreb (predecessor of GNK Dinamo Zagreb), a Croatian Association football club, is founded in Zagreb.
- April 27 – Huanghuagang Uprising: In China, rebels take five villages in an attempt to create a power base to fight Imperial rule; those who die are remembered as "The 72 Martyrs" (the event is also called the "Second Guangzhou Uprising" and the "Yellow Flower Mound Revolt").
- June 7 – Mexican Revolution: Francisco Madero arrives in Mexico City, just after the 1911 Michoacán earthquake.
- June 14 – RMS Olympic departs Southampton, England, for her maiden voyage, with a first call at Cherbourg, France.
- June 15 – RMS Olympic arrives in Queenstown, Ireland, to discharge and take up passengers.
- June 21 – RMS Olympic arrives in New York, United States, at the end of her maiden voyage. She proceeds to her quarantine station off Staten Island, which she leaves at 7:45 a.m., and is saluted on her way up New York Harbor by all kinds of craft, as she steams to Pier 59 in the North River. With the assistance of twelve tugs, Olympic is safely moored at 10 a.m.
- June 22 – George V is crowned King of the United Kingdom and the British Dominions, at Westminster Abbey in London. Moored at Pier 59 of New York Harbor, RMS Olympic is decorated for the occasion.
- June 25 – The Polish Football Union (PFU), later absorbed into the (Polish: Polski Związek Piłki Nożnej, PZPN), is founded.
- June 28 – RMS Olympic departs New York, for her maiden eastbound voyage back to Southampton, England.
- June 28 – The Nakhla meteorite falls in the Abu Hummus region of Egypt, providing evidence of water on Mars.
- June – The Sixth Conference of the International Woman Suffrage Alliance is held in Stockholm, Sweden.
- October 4 – China adopts "Cup of Solid Gold" as its first national anthem. However, it is never performed publicly and is replaced a few months later with a new composition.
- October 7 – Liberal leader Karl Staaff returns as Prime Minister of Sweden, after an Riksdag election victory based on the promises of defence cuts and social reforms.
- October 10 – The Wuchang Uprising starts the Xinhai Revolution, that leads to the founding of the Republic of China.
- October 16 – Mexican Revolution: Felix Diaz, nephew of Porfirio Díaz, occupies the port of Veracruz, as a sign of rebellion against Madero.
- October 26 – The Philadelphia Athletics defeat the New York Giants, 13–2, to win the 1911 World Series in 6 games. The game is tied 1–1 after three innings, but with four runs in the fourth, and seven runs in the seventh, the A's demolish the Giants. The most unusual play of the game is an inside-the-park home run made by the A's Jack Barry, on a bunt.
- November 1 – The world's first combat aerial bombing mission takes place in Libya, during the Italo-Turkish War. Second Lieutenant Giulio Gavotti of Italy drops several small bombs.
- November 3 – Chevrolet officially enters the automobile market, in competition with the Ford Model T.
- November 4 – The Treaty of Berlin brings the Agadir Crisis to a close. This treaty leads Morocco to be split between France (as a protectorate) and Spain (as the colony of Spanish Sahara), with Germany forfeiting all claims to Morocco. In return, France gives Germany a portion of the French Congo (as Kamerun) and Germany cedes some of German Kamerun to France (as Chad).
- November 5 – Italy annexes Tripoli and Cyrenaica (confirmed by an act of the Italian Parliament on February 25, 1912).
- November 17 – Omega Psi Phi Fraternity Incorporated (the first black Greek-lettered organization founded at an American historically black college or university) is founded on the campus of Howard University, in Washington, D.C.