in 1925

Ruins of the town of Griffin, Indiana.
The Tri-State Tornado hits the Midwestern states of Missouri, Illinois, and Indiana, killing 695 people.
The Tri-State Tornado of Wednesday, March 18, 1925, was the deadliest tornado in U.S. history. With 695 confirmed fatalities, the tornado killed more than twice as many as the second deadliest, the 1840 Great Natchez Tornado. The continuous ≥219 mile (≥352 km) track left by the tornado was the longest ever recorded in the world: the tornado crossed from southeastern Missouri, through Southern Illinois, then into southwestern Indiana. While not officially rated by NOAA, it is recognized by many as an F5 tornado, the maximal damage rating issued on the Fujita scale, and the rating is widely accepted by many.
in 1937
The New London School explosion kills three hundred, mostly children.
The New London School explosion occurred on March 18, 1937, when a natural gas leak caused an explosion, destroying the London School of New London, Texas, a community in Rusk County previously known as "London". The disaster killed more than 295 students and teachers, making it the worst catastrophe to take place in a U.S. school building.
in 1965
Cosmonaut Aleksei Leonov, leaving his spacecraft Voskhod 2 for 12 minutes, becomes the first person to walk in space.
Leonov had no means to control his motion other than pulling on his 50.7-foot (15.5 m) tether. After the flight, he claimed this was easy, but his space suit ballooned from its internal pressure against the vacuum of space, stiffening so much that he could not activate the shutter on his chest-mounted camera.
Deaths
in 1745
Robert Walpole, 1st Earl of Orford, known before 1742 as Sir Robert Walpole, was a British statesman who is generally regarded as having been the first Prime Minister of Great Britain. Although the position of "Prime Minister" had no recognition in law or official use at the time, Walpole is nevertheless acknowledged as having held the office de facto because of his influence within the Cabinet.

in 1964
Norbert Wiener was an American mathematician. He was Professor of Mathematics at MIT. A famous child prodigy, Wiener later became an early researcher in stochastic and noise processes, contributing work relevant to electronic engineering, electronic communication, and control systems. Wiener is regarded as the originator of cybernetics, a formalization of the notion of feedback, with many implications for engineering, systems control, computer science, biology, philosophy, and the organization of society.