Quackers are mysterious sounds, similar to a frog noise, widely reported by the crews of Soviet Navy submarines from various parts of the North Atlantic and Arctic Oceans during the peak of the Cold War, as well as their assumed sources. During the Cold War, when Soviet ballistic missile submarines went to patrol northern seas, their crews started reporting the mysterious frog-like sounds, which soon were dubbed "quackers", from the Russian rendition of a frog noise. These sounds appeared when submarines passed certain zones in the sea, and behaved as if they were emitted by some moving underwater object, which, however, failed to register on the active sonar. When the sub left their "patrol zone", the objects disappeared after emitting one final "quack". These objects exhibited behavior not unlike some living being or manned vessel, showing obvious interest in the passing submarine, circling around it, trying to actively avoid sonar pulses, and so on. The speed of some of these objects was in the range of 200 km/h, much higher than any then-known man-made vessel. Contact was attempted on several occasions, but, apart from some obvious reactions to these attempts (such as changing the pitch of the sounds or movement of the apparent sound source), nothing came of it.