In a little-known attempt to increase the flexibility of the B-58 as a weapons system, experiments were carried out in April 1964 under a program known as Operation Bullseye to see if the B-58 could carry and deliver conventional bombs. In coordination with Republic F-105Ds and McDonnell F-4C/Ds, sorties were flown using B-58s as lead ships and pathfinders and as independent strike aircraft. It was demonstrated that the B-58 could carry iron bombs on the wing root bomb racks that had earlier been added to accommodate four Mk. 43 nuclear weapons. Iron bombs of varying weights up to 3.000 pounds were dropped, usually from low altitudes and at speeds of 600 knots. Almost all of the drops were visual, with the AN/ASQ-42 system rarely being used. However, the fear that the B-58's integral wing tanks would make it vulnerable to ground fire during low-altitude delivery lead to the abandonment of the program.