Bad example.  Seeing is that the testimonies exist, I would say this shows that it would be exceedingly difficult to keep under wraps.  It's the risk that is significant.  There would need to be a substantial amount of people involved within layers of government outside of the initial small coterie of planners and conceivers.  All it would take was one leak, and boom, you're fucked.  That risk would have been huge-- it would have been likely.