In 1965 10 tornadoes hit 18 counties in north and central Indiana. This later became known as the Palm Sunday Tornado Outbreak, the deadliest in state history.
The tornadoes hit between 4:45pm and a little after 6:30pm. Seven of the tornadoes left 137 dead, and 1724 injured.
The National Weather Service in Northern Indiana has put together this summary of the event.
The National Weather Service office in Detroit has put together this analysis of the conditions that led up to this weather disaster.