During World War II, scientists on both sides were much concerned with the difficult problem posed by accurate navigation. However, as with so many war-time inventions, the consequent improvement in navigational methods were also used to drop bombs precisely and to guide long-range missiles to their distant targets. The subsequent development of early radio and radar guidance systems, today enables intercontinental rockets to be aimed with an accuracy of a few hundred yards from their intended target at a range of 8,000 miles.