Or they announce it to the world by using it.
How are they going to hit the US with an atomic weapon? They don’t have air supremacy anymore. They don’t have SLBMs, which are 15 years away from development.
By the Summer of 1944 (after Overlord), Germany had already rescinded flying their Heinkel HE 177 strategic bomber. The best bomber they had could fly 2k miles on a suicide mission with ordinance.
Ferry range is 3,480 miles. Brest to Boston is 3160 miles.
Little boy was 9700 pounds. Germany’s best bomber could carry 30k pounds fully loaded.
Combat radius was 957 miles. For a suicide one way mission, it would be 1914 miles. That would only get them 2/3rds of the way.
Just not possible for a German nuclear weapon strike on the United States with a strategic bomber in 1944.