John von Neumann died at the age of 53 at Walter Reed Army Medical Hospital in Washington, D.C., from cancer. He was buried at Princeton Cemetery. This date marks the end of the life of a monumental figure in mathematics, science, and technology.

John von Neumann was present as an eyewitness to the first test of an atomic bomb detonation, code-named Trinity. The event was conducted as a test of the implosion method device, at the Alamogordo Bombing Range in New Mexico. Based on his observation alone, von Neumann estimated the test had resulted in a blast equivalent to 5 kilotons of TNT (21 TJ) but Enrico Fermi produced a more accurate estimate of 10 kilotons by dropping scraps of torn-up paper as the shock wave passed his location and watching how far they scattered. The actual power of the explosion had been between 20 and 22 kilotons. It was in von Neumann's 1944 papers that the expression 'kilotons' appeared for the first time.