  During the Manhattan project a simple formula was developed by Bethe and
Feynman in 1943 to estimate the yield of a fission-only nuclear explosion of a
uniformly-dense bare-sphere of supercritical fissile material. We have not
found any evidence that Bethe and Feynman knew of the first yield formula
obtained by Frisch and Peierls contained within their famous March 1940
memorandum. Similarly, we have not found any technical documents that compare
the Bethe-Feynman formula to the earlier works of Frisch and Peierls, or
Serber. After adjusting for differences in the labeling of critical radii, we
find that earlier formulas only differ by a scaling factor.
