Specifically, they both used what was listed in a later report as the 991 and 992 "Gun Cores." The 991 and 992 cores could also be used in the W19 nuclear artillery shell, and the 992 core could be used in the W33 artillery shell. "History of the Custody and Deployment of Nuclear Weapons, July 1945 through September 1977"(PDF). Office of the Assistant to the Secretary of Defense. February 1978. p. E-2.