A German historian has found possible information that points to the Nazi's detonating a small 'hybrid' nuclear weapon on the 3rd of March 1945 at Thuringia which destroyed an area of about 500 sq m - killing several hundred prisoners of war and concentration camp inmates. The full story can be found here
http://news.bbc.co.uk/2/hi/europe/4348497.stm. As is said there is much sceptism about this from historians and others a like.