Geneticist George Beadle and biochemist Edward Tatum formulate the one gene-one enzyme hypothesis.

Engineers J. Presper Eckert, Jr., and John W. Mauchly complete the ENIAC (Electronic Numerical Integrator and Calculator), the first successful automatic electronic digital computer.

In the Trinity Test, the first atomic bomb is tested at Alamogordo, New Mexico.

6 Aug.

The first atomic bomb used in warfare, an American uranium bomb, is dropped on Hiroshima, Japan, killing more than fifty thousand.

9 Aug.

Americans drop a plutonium atomic bomb on Nagasaki, Japan, killing more than forty thousand.