Recently, U.S. President Donald Trump made headlines when he told the Pentagon to resume testing of U.S. nuclear weapons, citing his concerns that countries like China or Russia had supposedly conducted secret underground nuclear weapons tests and that the United States was falling behind.

While the American president’s post created much controversy around the nature of such tests, the U.S. energy secretary later explained that Trump’s planned tests would not include any actual nuclear explosions, but would encompass “system tests” to verify the state of American nuclear arsenals.

While the fact that the United States does not plan to detonate nuclear weapons is reassuring, the country, as well as China and Russia, have a long history of experimenting with real nuclear weapons to measure the performance of their devastating arsenals.