This morning in 1963, as 3 workers were moving partially-disassembled high-explosive assemblies into storage igloo 572 at the Medina Modification Center near San Antonio, Texas (one of six original AEC nuclear stockpile sites), a spark ignited some conventional high explosives.

Seeing the fire, the workers—Louis Ehlinger, Sr. (below), Hilary Huser, and Floyd Lutz—immediately ran for cover. About 45 seconds later, 123,000 pounds of chemical high explosives in the igloo exploded, creating a huge mushroom cloud. Miraculously, no one was seriously injured.

The blast dug out a crater 20-feet deep and 120-feet wide and dispersed natural and depleted uranium in the nuclear weapon components stored in the igloo. The shockwave broke windows 12 miles away in downtown San Antonio and was heard at least 50 miles away.

The size of the blast and the mushroom cloud initially led workers at the site (and at adjacent Lackland AFB) to fear a nuclear explosion had occurred. Although Medina's nuclear mission was not public knowledge, there were suspicions and nearby residents shared the same concern.

This serious accident would have lingered longer in the public consciousness if not for the assassination of President John F. Kennedy in Dallas 9 days later. In 1965, the AEC moved all nuclear weapons modification and disassembly work from Medina to the Pantex Plant in Amarillo.