Countdown to The Cold War: Trinity

Seventy years ago, at a site near Alamogordo, New Mexico, a new era in human history was birthed into existence. At approximately 5:30 a.m. Mountain War Time (MWT) on July 16, 1945, the first atomic bomb was detonated.

Trinity Explosion

In the pre-dawn hours of that long-ago July morning, a rainstorm passed through the area of the impending test. Thunder and lightning filled the skies, and members of the test crew fretted that the test might be delayed or, worse, that lightning might strike the 100-foot tall tower atop which the bomb was perched, damaging the bomb. Perhaps, the bomb might be inadvertently set off.

The weather had long been a concern of the group of scientists, engineers, and military men responsible for conducting the test. In “The Test at Trinity,” a chapter of Critical Assembly by Lillian Hoddeson, et al., the authors say this of the weather:

The date of the Trinity test depended both on the readiness of the components and the weather. In the early months of 1945, gadget parts promised to be ready in June or July. The questions was, when would the weather conditions be appropriate? Haze, dust, and mirage effects would interfere with photographic measurements; overcast skies would make flying more difficult for the airplanes that would drop the instruments. Thunderstorms would wreak havoc with the barrage balloons. Winds had to be favorable to keep the radioactive cloud away from inhabited areas to the east and north.

This level of attention to the weather was, in part, made necessary by all of the various pieces of testing equipment that would be employed to monitor and analyze the explosion. To measure the strength of the atom bomb explosion, piezoelectric, aluminum diaphragm, and airborne condenser gauges were to be employed at the Trinity site. These gauges and other aspects of the test program were validated on May 7, 1945 in the so-called “100-ton test,” which actually used 108 tons of TNT. Radioactivity detection gear was calibrated by including a small amount of radioactive material—plutonium created in the Hanford reactor—in among the thousands of crates of TNT. The plutonium was dispersed by the explosion; it didn’t contribute to the explosion in any fashion. Among the more unique parts of the test protocol that were exercised during the 100-ton test was a lead-lined Sherman (M-4) tank. After the actual Trinity test, the tank was used to retrieve radioactive samples of earth from the blast area.

The storms on the night of the test made it obvious that the scientists had been right to be concerned about the weather. But, another passage in Critical Assembly makes it clear that there was little to be done:

Meeting the weather needs of all groups proved impossible. The pit assembly team’s request for humidity below 89 percent and Anderson’s for no rain after the shot were easy to meet in the desert. But the groups had to compromise on wind needs. Manley requested calm air for his blast gauges. Holloway and Morrison of the pit assembly group also wanted little or no wind, to avoid dust in the air at the base of the tower. In contrast, Bainbridge asked for 10- to 15-mph winds to carry the cloud away from Ground Zero and to help disperse it.

Around 450 personnel were present at the Trinity test. As the night wore on, the test was delayed in an attempt to wait for the weather to clear. It was rescheduled for 5:30 a.m. MWT. The scientists who were present busied themselves as best they could. Much to the discomfort of some of those present, physicist Edward Teller slathered sunblock on his face and arms and then offered it to others. Nobel prize winner Enrico Fermi tore a piece of paper into shreds. He planned to use them in a simple experiment to test the size of the blast.

Oppenheimer and Groves at Trinity Site (U.S. Army Corps of Engineers)

The bomb went off, and, as the blast wave passed through the viewing area, Fermi dropped the shreds of paper from his hand and watched as they fluttered along, carried the moving air. He calculated the blast’s size at approximately ten kilotons (ten thousand tons of TNT). He was quite close for a physicist making an estimate based on such a rough—yet, somehow, simultaneously elegant—measurement. Later analysis would put the bomb’s strength at about twenty to twenty-two kilotons.

In the moment, physicist Kenneth Bainbridge, Trinity’s test director, reportedly said, “Now we are all sons of bitches.” That quote appears in a number of places, including a guest post written by Claire Robinson May, Bainbridge’s granddaughter.

Physicist Phil Morrison—who would later direct the dissertation of our Chapman University colleague, Menas Kafatos—once said in a documentary that he was taken aback when he realized that the light and heat on his face warmed it like the morning sun.

We will discuss some of the fallout, literal, figurative, and pun-intended in next week’s post. In the meantime, check out pour previous posts about Trinity; Trinity & Apollo and A Day with Two Suns.