World War II: Navigation errors lead to an accidental American bombing of the Swiss city of Schaffhausen.

World War II or the Second World War was a global conflict between two coalitions: the Allies and the Axis powers. Nearly all of the world's countries participated, with many nations mobilising all resources in pursuit of total war. Tanks and aircraft played major roles, enabling the strategic bombing of cities and delivery of the first and only nuclear weapons ever used in war. World War II is the deadliest conflict in history, causing the death of 70 to 85 million people, more than half of whom were civilians. Millions died in genocides, including the Holocaust, and by massacres, starvation, and disease. After the Allied victory, Germany, Austria, Japan, and Korea were occupied, and German and Japanese leaders were tried for war crimes.

During World War II, the neutral country of Switzerland underwent initially sporadic bombing and aerial combat events that became more frequent during the later stages of the war.

Schaffhausen, historically known in English as Shaffhouse, is a town with historic roots, a municipality in northern Switzerland, and the capital of the canton of the same name; it has an estimated population of 36,000 as of December 2016. It is located right next to the shore of the High Rhine; it is one of four Swiss towns located entirely on the northern side of the Rhine, along with Neuhausen am Rheinfall, the historic Neunkirch, and medieval Stein am Rhein.

April 1 is the 91st day of the year in the Gregorian calendar; 274 days remain until the end of the year.