That would have been the fourth atomic bomb. The first was the Trinity detonation. Second was Hiroshima. Third was Nagasaki. FWIW. You can see the fourth g

That would have been the fourth atomic bomb. The first was the Trinity detonation. Second was Hiroshima. Third was Nagasaki. FWIW. You can see the fourth gadget at the National Museum of Nuclear Science & History in Albuquerque.