To clarify a point: you'd get a better response if you asked, "what is the history of keeping the identity of executioners secret?" Because that's your actual interesting question here (and I don't know the answer to it).

The atomic bomb connection is a total red herring: soldiers' identities are not kept secret in war, and that applies to the atomic bombing as well (as well as any other bombing, or use of artillery shells, or use of machine guns, and so on).