Cin Qipinsar WINGINILE i Dhp-seenae. Mark13. (Imploston-type bomb; previously designated "Improved 60-ineh weapon. } 22. Possible improvements to the Mark 6 bomb which are under considvration for the future were mentioned in the preecding progress report. The cffort at this stage consists principally of work on new components, for example the external initiator. Increasing the length of the bomb from 128 inches (the length of the Marks 4 and 6G) to 145 inches is desirable, but this is controlled by bomb bay size in aircraft. The date when aireraft with larger bomb bays will become available in sufficient mumbers therefore influences the design of the weapon. Stockpiling of the Mark 13 is tentatively scheduled to begin early in 1954. 23, Other major development activities in the field of fission weapons are 25 follows: 32h. Uranium 232. ean tk nma4 which, Uranium 233 is a fissionable material in ordinary implosion weapons, would probably be somewhat less effective than plutonium but considcrably more effective than U 2 / ~ 12 . TY yp-SeeRie AO? STEXCINIG I