Goldberg wrote that ordinary delivery vans were used. That doesn't rule out a pack of concealed security men, I suppose.
But the Atlantic article also points out that weapons were being transported this way whole - completely assembled with fuel and triggering mechanisms. That means someone could easily arrange the theft of a nuclear weapon - or, if inferior designs are used, the bomb could partially explode in a vehicle collision. (I recall a newspaper story of one Chinese pilot who said his colleagues greatly feared the hydrogen bomb his aircraft was carrying could explode not just in a collision but due to static electricity.)
Is there anyone other than the SPD who evaluates the risks of their new procedures to the bombs themselves?