http://www.thewebfairy.com/missilegate/rfz/rocket.htm
Description:
"The article's description of the nuclear cannon is correct. This was a German invention and was under development in Germany during the latter stages of the war. A prototype was even built and it carried the German designation of DKM 44 (1). This very cannon was copied by the Americans and became the T-131 which fired a nuclear warhead (2)."
It claims that germans developed a nuclear cannon and US later copied it. To me, this seems to be just another addition to nazis-invented-everything/UFO myth. There might have been plans for DKM-44, but i really doubt that it was meant to be nuclear.