They would have found it difficult to do so. This being a nuclear question, we of course turn to the efforts of u/restricteddata:

• This post examines Enola Gay's 'defensive' measures;
• and this examines the bombing crews, but the following discussion also examines the air defence circumstances at the time, with relevant contributions from u/jschooltiger and u/insane_contin.

And should anyone else have further insight on the matter, go right ahead and post away!