On this day in 1886, members of labor organizations and industrial workers from the United States and Canada held a mass rally in Chicago demanding shorter working hours. Three years later, in 1889, an international labor union would designate May 1 as International Labor Day.
On this day in 1927, the first cooked meals on a scheduled flight were introduced on an Imperial Airways flight from London to Paris.
On this day in 1956, the polio vaccine developed by Dr. Jonas Salk was made available to the public.
On this day in 1961, the Prime Minister of Cuba, Fidel Castro, proclaimed Cuba a socialist nation and abolished elections.
On this day in 2011, US President Barack Obama announced that Osama bin Laden, the suspected mastermind behind the September 11 attacks, had been been killed by US special forces in Pakistan.