The polio vaccine is declared safe and effective.
7 April 1922
United States Secretary of the Interior leases Teapot Dome petroleum reserves in Wyoming in what becomes known as the Teapot Dome Scandal
5 April 1958
Ripple Rock, an underwater threat to navigation in the Seymour Narrows in Canada is destroyed in a controlled explosions
4 April 1944
The bombardment of Bucharest by Anglo-American forces results in 3000 civilian deaths.