The Road to Trinity

Nuclear Age Begins 75 Years Ago

Over the course of about 28 months (April 1943 – July 1945), the Laboratory developed two types of nuclear weapons. Little Boy, the gun-type weapon, did not undergo a full-scale nuclear test, but the implosion type weapon, Fat Man, famously did.

Although the Manhattan Project scientists were fairly confident that the Fat Man design would work, they weren’t confident enough to drop a significant portion of the world’s supply of plutonium over enemy territory. The decision to test was made, leading to what would become Trinity – the world’s first nuclear explosion.

Location, Location, Location

Physicist Kenneth Bainbridge was chosen as the test director for Trinity. Meanwhile, the U.S. Army needed to find a suitable location to conduct the test, and a list of requirements was created by Bainbridge. The site would need to be flat and isolated and have consistently good weather; no Native Americans could be displaced. It also needed to be close to Los Alamos for ease of transportation and land acquisition. With these considerations in mind, several possible sites were selected.

Bainbridge chose Jornada del Muerto, about 200 miles south of Los Alamos. As a part of the Alamogordo Bombing and Gunnery Range, the location was already owned by the government, and it was near Los Alamos, but not so close that people would suspect it was connected to the Lab.

Poetry and Plutonium 

Years later, in 1962, Gen. Leslie Groves wrote J. Robert Oppenheimer asking why the name “Trinity” was chosen. In his reply, Oppenheimer recalls that he had been reading John Donne’s poetry around the time of the test and was inspired by the line: “Batter my heart, three person’d God.”

Leading up to the test, there was some concern that the high explosives in the device would go off, but there would be no nuclear yield. If this happened, a large portion of the world’s supply of plutonium would be strewn across the desert floor, and scientists wanted to be able to collect this rare material.

A concrete bowl was one idea that was explored for this purpose. A large, gently sloping concrete bowl would be constructed and filled with water. This would catch the dispersed plutonium, which would be collected as the bowl was drained. Although no concrete bowl was built at the Trinity site, a smaller model was constructed at Los Alamos.

Jumbo was another option for containment. Jumbo was a steel container built to withstand the force of a conventional explosive and contain the plutonium in the event of a failure. If the device was successful, Jumbo would be vaporized. Small-scale testing of “Jumbinos” took place at Los Alamos, and a full-size Jumbo vessel weighing more than 200 tons was built. Jumbo was built by the Babcock and Wilcox Steel Corporation of Ohio and was painstakingly transported to the Trinity site, though it was ultimately not used.

Keeping Secrets

As always, the secrecy and security of the site were important considerations. Many of the enlisted personnel stationed at the Trinity site did not know the purpose of the site that was being patrolled by military police. In order to keep the secret of the bomb after the Trinity test, two press releases were prepared in advance. One release stated that a munitions dump had exploded at the bombing range. There was some concern that the surrounding areas would need to be evacuated due to fallout, so the second press release stated that a munitions dump containing gas shells had exploded and some nearby populations may need to be temporarily evacuated.

Two large-scale experiments took place in preparation for the Trinity test. On May 7, 1945, several months before Trinity, just over 100 tons of TNT were detonated at the site, along with a radioactive tracer, to calibrate the equipment for Trinity and practice the timing of the test.

A full-scale mock-up of Fat Man (the implosion weapon) without the nuclear material was detonated on July 14, 1945, just two days before the Trinity test. The Creutz test, conducted by physicist Edward Creutz, took place at TA-18 in Los Alamos. The initial results were concerning – they indicated that Trinity wouldn’t work. Luckily, physicist Hans Bethe, leader of T Division and future Nobel laureate, realized that the results had been calculated incorrectly. Trinity would, theoretically, be successful after all.

The Nuclear Age Begins

As the Trinity test day approached, assembly of the Gadget, which the device was nicknamed, began.

There were some tense moments during the preparation. When the engineers tried to place the plutonium into the device, it didn’t fit because it had expanded due to the heat. The sphere was put in the shade to cool, and soon fit into the device. The Gadget was raised onto a 100-foot steel tower in anticipation of the test scheduled for 4 a.m., July 16, 1945. The morning of the test, however, brought thunderstorms, and the test was delayed for almost an hour and a half.

Finally, despite the setbacks and challenges, years of research and effort at the secret laboratory in Los Alamos, New Mexico, culminated at 5:29 a.m.

The Gadget’s detonation was accompanied by an intense flash of light and a wave of heat, followed by a loud burst that echoed for miles. A ball of fire surrounded by a giant mushroom cloud stretched 3,280 feet wide and then rose in a column of smoke to a height in excess of 40,000 feet. The Gadget’s power – equivalent to around 21,000 tons of TNT – destroyed the tower on which it had been placed.

Immediate feelings reportedly ranged from surprise to relief to jubilance to dread, with a common hope that World War II would be over soon.