Active sonar has been back in use for searching for submarines for a few decades now, the article is out of date. Low frequency active sonar towed sonars are fitted to modern submarine hunting ships; the low frequency is necessary to get a long range as higher frequencies are heavily attenuated. If you've seen news stories about the danger to marine mammals from military sonar it was these systems that were involved, as they put large amounts of energy into the frequency bands that propagate well - these bands being the most useful for whales to communicate with as well.
eg: https://en.wikipedia.org/wiki/Sonar_2087