Nevertheless I have to imagine there are serious barriers to putting an actual nuclear bomb on an unmanned aircraft. Just as our nuclear missile silos are still manned, you want a human(s) at the button as close to the bomb as possible, to avoid accidents resulting from errant, erratic or unexpected behavior, or to be able to clean up after them before they lead to the apocalypse.

Imagine if an unmanned bomber was sent on a mission and you lost contact. There was a movie (Fail Safe) about a manned bomber that happened to and it was scary enough