The bomb was dropped by an MC-130 aircraft, stationed in Afghanistan and operated by Air Force Special Operations Command. The strike targeted tunnels and caves used by ISIS. The Achin district is the primary center of ISIS activity in Afghanistan. “The U.S. takes the fight against ISIS very seriously,” the White House Press Secretary Sean Spicer said during the daily briefing. Military officials did not immediately know how many ISIS fighters were killed or if any civilians died in the attack. Hans Kristensen, director of the nuclear information project at the Federation of American Scientists, said the explosive power of even the smallest nuclear weapon in the U.S. arsenal, the B-61 bomb, is “an order of magnitude” larger than the GB-43, the largest non-nuclear bomb the U.S. has available.