Four days after North Korea conducted its latest nuclear weapons test in January, the United States flew a B-52 bomber over South Korea. This show of force by the U.S. challenged North Korea's insistence that it had tested a hydrogen bomb, as if to say: "So you say you tested a hydrogen bomb? Well, then, let us show you a real hydrogen bomb." B-52s are capable of carrying hydrogen bombs.
B-52 bombers are also loaded with highly destructive "bunker busters" — bombs that can penetrate deep into the ground. The B-52 flight over South Korea also sent the message that, if necessary, the bombers could destroy North Korea's underground military facilities, of which there are reportedly more than 5,000.
Such a U.S. response likely came as no surprise to North Korea. The Korean Central News Agency quoted North Korean leader Kim Jong Un as describing the recent test as "a self-defensive step for reliably defending the peace on the Korean Peninsula and the regional security from the danger of nuclear war caused by the U.S.-led imperialists."