On August 9, 1945, the B-29 Bockscar took off from Tinian Island and flew to Nagasaki, Japan, where it delivered the worlds third atomic weapon. The fissile material in the bomb, dubbed Fat Man because of its shape, had been created and refined at Hanford, Washington. The first production reactor began sustained reaction in September of 1944, though shortly the reaction ceased because of Xenon poisoning. Soon the pile was back up to speed thanks to Dupont safety margins.
I had the opportunity to visit this reactor yesterday! It is a National Historic Landmark and a Museum of the Manhattan Project. I went with a friend I grew up with and we managed to be on the correct tour so I could take my camera. Here's some of what I got.