For low-altitude detonations much of the fallout comes from irradiated dirt. For example the Baker nuclear test was the first sub-surface nuke and resulted in h

For low-altitude detonations much of the fallout comes from irradiated dirt. For example the Baker nuclear test was the first sub-surface nuke and resulted in heavy radioactive contamination of the test ships. https://en.m.wikipedia.org/wiki/Operation_Crossroads https://en.m.wikipedia.org/wiki/Operation_Crossroads