| 41971 | April 12 | Event | 1606 – The Union Flag is adopted as the flag of English and Scottish ships. |
| 41972 | April 12 | Event | 1776 – American Revolution: With the Halifax Resolves, the North Carolina Provincial Congress authorizes its Congressional delegation to vote for independence from Britain. |
| 41973 | April 12 | Event | 1820 – Alexander Ypsilantis is declared leader of Filiki Eteria, a secret organization to overthrow Ottoman rule over Greece. |
| 41974 | April 12 | Event | 1831 – Soldiers marching on the Broughton Suspension Bridge in Manchester, England cause it to collapse. |
| 41975 | April 12 | Event | 1861 – American Civil War: The war begins with Confederate forces firing on Fort Sumter, in the harbor of Charleston, South Carolina. |
| 41976 | April 12 | Event | 1862 – American Civil War: The Andrews Raid (the Great Locomotive Chase) occurs, starting from Big Shanty, Georgia (now Kennesaw). |
| 41977 | April 12 | Event | 1864 – American Civil War: The Battle of Fort Pillow: Confederate forces kill most of the African American soldiers that surrendered at Fort Pillow, Tennessee. |
| 41978 | April 12 | Event | 1865 – American Civil War: Mobile, Alabama, falls to the Union Army. |
| 41979 | April 12 | Event | 1877 – The United Kingdom annexes the Transvaal. |
| 41980 | April 12 | Event | 1910 – SMS Zrínyi, one of the last pre-dreadnought battleships built by the Austro-Hungarian Navy, is launched. |
| 41981 | April 12 | Event | 1917 – World War I: Canadian forces successfully complete the taking of Vimy Ridge from the Germans. |
| 41982 | April 12 | Event | 1927 – Shanghai massacre of 1927: Chiang Kai-shek orders the Communist Party of China members executed in Shanghai, ending the First United Front. |
| 41983 | April 12 | Event | 1927 – Rocksprings, Texas was hit by an F5 tornado that destroyed 235 of the 247 buildings in the town and killed 72 townspeople and injured 205 third deadliest tornado in Texas history. |
| 41984 | April 12 | Event | 1928 – The Bremen, a German Junkers W 33 type aircraft, takes off for the first successful transatlantic aeroplane flight from east to west. |
| 41985 | April 12 | Event | 1934 – The strongest surface wind gust in the world at the time of 231 mph, is measured on the summit of Mount Washington, New Hampshire. It has since been surpassed. |
| 41986 | April 12 | Event | 1934 – The U.S. Auto-Lite strike begins, culminating in a five-day melee between Ohio National Guard troops and 6,000 strikers and picketers. |
| 41987 | April 12 | Event | 1935 – First flight of the Bristol Blenheim. |
| 41988 | April 12 | Event | 1937 – Sir Frank Whittle ground-tests the first jet engine designed to power an aircraft, at Rugby, England. |
| 41989 | April 12 | Event | 1945 – U.S. President Franklin D. Roosevelt dies while in office Vice President Harry Truman, becomes President upon Roosevelt's death. |
| 41990 | April 12 | Event | 1945 – The U.S. Ninth Army under General William H. Simpson crosses the Elbe River astride Magdeburg, and reached Tangermünde—only 50 miles from Berlin. |
| 41991 | April 12 | Event | 1955 – The polio vaccine, developed by Dr. Jonas Salk, is declared safe and effective. |
| 41992 | April 12 | Event | 1961 – The Soviet cosmonaut Yuri Gagarin becomes the first human to travel into outer space and perform the first manned orbital flight, Vostok 1. |
| 41993 | April 12 | Event | 1963 – The Soviet nuclear-powered submarine K-33 collides with the Finnish merchant vessel M/S Finnclipper in the Danish straits. |
| 41994 | April 12 | Event | 1970 – Soviet submarine K-8, carrying four nuclear torpedoes, sinks in the Bay of Biscay four days after a fire on board. |
| 41995 | April 12 | Event | 1980 – Samuel Doe takes control of Liberia in a coup d'état, ending over 130 years of minority Americo-Liberian rule over the country. |
| 41996 | April 12 | Event | 1980 – Terry Fox begins his "Marathon of Hope" at St. John's, Newfoundland. |
| 41997 | April 12 | Event | 1981 – The first launch of a Space Shuttle (Columbia) takes place - the STS-1 mission. |
| 41998 | April 12 | Event | 1990 – Jim Gary's "Twentieth Century Dinosaurs" exhibition opens at the Smithsonian Institution National Museum of Natural History in Washington, D.C. He is the only sculptor ever invited to present a solo exhibition there. |
| 41999 | April 12 | Event | 1992 – The Euro Disney Resort officially opens with its theme park Euro Disneyland. The resort and its park's name are subsequently changed to Disneyland Paris. |
| 42000 | April 12 | Event | 1994 – Canter & Siegel post the first commercial mass Usenet spam. |