The church my parents attend was one of the first ones in town, first organized during the war. Several members of their church were deeply involved in the production - but because of the compartmentalization of information, they didn't realize what it was they were building. They knew it was a bomb, they knew that hopes were high that it would end the war quickly - but they had no idea of the magnitude of the device. I've had some in-depth conversations with quite a few of them, and every single one of them says that they have no regrets whatsoever over what they worked on.
I've worked with with Dr. Alvin Weinberg on a few occasions. Dr. Weinberg was head of the X-10 (now ORNL) Physics Division during the war. Dr. Weinberg explained to me one time that at first, he urged that the atomic bomb not be dropped on a populated area, but rather just demonstrated. He says that he thinks differently now. He believes that it did end World War II earlier, and saved lives on both sides of the fighting.
Regrets? Here in Oak Ridge? Only from those that come here to protest that had nothing to do with the war - and they don't count for sh_t.
Okay. Not arguing the merits of dropping or not dropping it, one (and that *one* may be a country) reaps what he/she/it sows...multiplied, pressed down, shaken together...and Hiroshima was a whale of a lot of sowing.
Recommendation: All should walk humbly (versus proudly) before God less reaping come quickly. Da 12:10.