Why were Los Alamos scientists so confident “Little Boy” would work?

Question

The 1945 Trinity test was run to prove the complicated “Fat Man” design would even work. But why were scientists so confident of the “Little Boy” design that the didn’t feel the need to do a full test of the design? The design was simpler, but still, no one had ever done it before. Was it purely for time? Lack of materials? Or was the design and principles so sound, it couldn’t fail?

In: 11

Answer 1

A lot of answers here have good points, but what they fail to consider is material availability. They simply didn’t have enough uranium for a test. The “Little Boy” bomb uses U-235 to explode. The “Fat Man” uses Plutonium. U-235 is a lot harder to make than Plutonium. In fact, you make Plutonium using the waste material of U-235 extraction. As such, in July 1945, they had enough material for 3 bombs – two “Fat Man” and one “Little Boy”. Then the logic become obvious as to why they tested “Fat Man” – it was the only spare they had to work with