Though the practice is illegal in international law, some deep-sea salvagers are targeting sunken WWII-era ships because they are made of steel produced before the use of nuclear weapons. Decades of open-air nuclear testing means all steel produced today has trace amounts of radiation, not enough to be unhealthy but enough to cause interference with scientific instruments. The steel of the WWII-era ships does not have this radiation, making it extremely valuable for medical and scientific testing.