I recently read My Enemy's Ally by Buettner. It's a Nazi WI. In the novel, some in the German government realize that Heisenberg either doesn't have the competence to spearhead the Nazi A-bomb or he'll subtly sabotage it so they decide to have a secret program to build one. In addition, since they need a delivery method they have the Horten Brothers build a intercontinental bomber as a one-off. I think that it was an interesting story, but very improbable.