Just for clarification jldjs, had you looked at your crew page, and there were no slots for a deck gun crew, or you looked on the hardware page, and no gun listed on the boat, or no gun listed in the left-hand column (inventory), or all of the above, or a combination? In my particular "find", there were "none of the above"... hence the "fix" above, which is based off of coletrains' method, with additions and edits for FotRSU...
