We report the basis for new estimates of “free-in-air” kermas resulting from the nuclear explosions at Hiroshima and Nagasaki for ground ranges out to 2 km. The results are substantially different from previously accepted values known as T65D, particularly for Hiroshima. The methodology used in our study is different from that of T65D. To obtain prompt neutron and gamma-ray kermas, calculated leakage spectra were utilized that had been generated by modern weapons design codes. These leakage spectra were used as sources in radiation transport calculations performed with extensively validated modern transport codes. We have further cross-checked our calculational results in one and two dimensions, and by using very different solution techniques. For delayed gamma rays, we used a formalism based on the results of atmospheric testing. Our results have been compared with Japanese in situ measurements of neutron activation and of gamma-ray kerma, and found to show good agreement with them. We have explained the major differences between the T65D values and our own, as well as between neutron kermas inferred from the in situ activations and our kerma values. These new results merit confidence. However, improvements in these estimates can occur when additional work is done. One application of practical importance to radiological protection standards has already been made.