Jumbo
The caption reads “Jumbo on a special railroad car at Pope, NM, waiting to be transported to Trinity Site in July [actually June] of 1945.” 
Jumbo was shipped from Ohio by rail and hauled to the site across 30 miles of desert on a specially built 64-wheel trailer. 
Moving Jumbo from its railcar required very careful and precise movements. At 214 tons, any misstep could result in loss of equipment, injury, or death. 
The 64-wheel trailer was pulled by several tractors in the front and rear. 
Trinity Site personnel pose in front of Jumbo and its trailer. Even though the trailer was custom-made to transport Jumbo, it still required several layers of lumber to cushion and evenly distribute the weight across the trailer’s surface. 
As confidence in the bomb’s ignition design grew, Trinity’s scientists and engineers decided that Jumbo would not be necessary. 
Jumbo was instead placed under a steel tower 800 yards west from ground zero. 
Jumbo was lowered with one end resting on the ground on top of an explosive charge. 
The Trinity explosion destroyed the tower but left Jumbo intact. 
The Army detonated eight 500-pound bombs inside Jumbo. Both ends were blown off, but the rest of it was left intact. 
In 1979, the Army moved Jumbo to the spot near the Trinity Gate, where it remains today.
There was a concern that if the explosion was successful, but the nuclear chain reaction did not follow, the 13 pounds of scarce and dangerous Plutonium would be blown all over the countryside. To contain the Plutonium if this happened the project designed a huge steel container. Several manufacturers reviewed the specs and refused the task. Steel fabricator Babcock and Wilcox of Ohio took the job in August 1944 and completed it in April 1945.
Named Jumbo, the container weighed 214 tons, was 25 feet long, 12 feet in diameter, had 15-inch thick walls comprised of 6-inches of steel plate and 9-inches of steel banding, and cost $12 million. Babcock and Wilcox moved Jumbo to Pope, New Mexico on a specially designed rail car. It was then transported 30 miles to a spot 800 yards northwest of ground zero on a special 64-wheel carrier. When loaded, it was pulled by a team of tractors to its front and rear.
The scientists and engineers decided to forego using Jumbo during detonation due to confidence in the bomb design, the potential to use increased quantities of plutonium without Jumbo, and concerns about how Jumbo would affect test results. Instead, it was placed under a steel tower, loaded with eight 500-pound bombs, lowered with one end resting on the ground, and detonated. The blast destroyed the tower and blew both ends off Jumbo. The rest of it was left intact. In 1979, the Army moved Jumbo to the spot near the ground zero gate where it is today.