I mean, do nuclear weapons actually work? In the YS2 we knew it was largely empty with a lot of electrical gubbins and a big dustbin inside, but was there anything in it?
Yep, a British built "Red Snow" warhead based on US B-28 design and some ballast. You could have got 4 US B-28's in a Vulcan, but the ballistic data for the original YS bomb was already known so it was quicker to modify the YS bomb casing to hold the smaller US warhead than to modify the NBS to drop the B-28 in its US configuration (according to a discussion in the latest RAFHS journal which covers the development of British nuclear weapons for the RAF as one of its topics).