When the 8 Valiants were modified in readiness for Op Grapple the outer wings were strengthened by double skinning (hence the multiple rows of rivets securing the extra skin). At the time it was suspected that the aircraft may have experienced severe turbulence as a result of the blast catching up with the departing aircraft - I believe all previous weapons tests had been carried out with the "bomb" mounted on a tower - this was to be the first air drop.