During the Cold War, Soviet submarines operated across the North Atlantic, Arctic, Pacific, and other strategic waters while increasingly sophisticated hydroacoustic systems were used to identify vessels and other underwater activity. Within that environment, Soviet submarine personnel later described encountering unusual sounds that could not readily be classified using the acoustic knowledge available to crews at the time. The phenomenon became known informally as the kvakery, usually translated as “Quackers,” because many of the reported sounds resembled prolonged frog-like croaking.

One of the most detailed surviving public accounts is attributed to V. T. Kulinchenko, identified as a Soviet Navy captain first rank, submarine veteran, and senior officer of the Navy Main Staff during the 1970s. Kulinchenko recalled that by the mid-1970s captains of nuclear-powered missile submarines returning from Atlantic patrols were submitting reports concerning unfamiliar noise sources that naval acousticians could not identify. According to the retrospective account, the sounds varied in duration and tone, although many resembled a long croak and eventually acquired the “Quacker” nickname.

Another account is attributed to A. N. Korzhev, also identified as a captain first rank and former commander of a Soviet nuclear submarine. Korzhev associated the increasing number of detections with the introduction of newer submarines equipped with more capable hydroacoustic systems. This raises an important possibility that at least part of the phenomenon became noticeable not because a new sound source suddenly appeared, but because improved Soviet equipment began detecting underwater sounds that earlier systems had missed or could not distinguish.

The reported acoustic behavior became the most unusual component of the story. Kulinchenko described sounds arriving from changing directions and varying in pitch, sometimes creating the impression that the source moved around a submarine. Some crews reportedly believed that the acoustic source accompanied their vessels for extended periods and then disappeared after a submarine left a particular area. Such observations encouraged interpretations involving deliberate or responsive behavior. However, descriptions such as “circling,” “following,” or “trying to communicate” represent interpretations of changing acoustic bearings and signals rather than direct visual observations of a physical object.

Later accounts also attribute extraordinary apparent speeds to the supposed acoustic sources. These claims are especially difficult to evaluate because publicly accessible material does not presently provide the original sonar plots, calculation methods, hydrophone data, or vessel logs from which such speeds were derived. A changing acoustic bearing does not by itself establish the existence, range, size, or velocity of a discrete underwater vehicle. Claims that the Quackers represented objects capable of traveling at speeds impossible for known submarines should therefore remain attributed to later testimony unless surviving operational data can be located.

The phenomenon reportedly attracted the attention of Soviet naval command. Kulinchenko's retrospective account states that a special group was created within Soviet naval intelligence under the authority of Navy commander-in-chief Sergey Gorshkov, with the knowledge of Defence Minister Andrei Grechko, to investigate the Quackers. The account places establishment of this effort in the late 1960s, while describing systematic submarine reports becoming conspicuous during the mid-1970s. That chronology requires further investigation, and until underlying orders, reports, or archival material are located, the existence and precise scope of the program should be treated as participant testimony rather than as independently reconstructed Soviet administrative history.

A natural intelligence concern during the Cold War was that the sounds might originate from Western anti-submarine warfare or surveillance technology. The United States and NATO were developing extensive systems for detecting and monitoring Soviet submarines, and the American SOSUS hydrophone network formed part of that strategic environment. Later Russian treatments consequently describe secret Western surveillance technology as one hypothesis considered for the unusual acoustic contacts. No publicly available evidence located for this Case File currently establishes that a Western system was responsible for the Soviet reports.

Biological explanations have also attracted substantial attention. Oceans contain numerous animals capable of producing powerful, complex, repetitive, or previously unfamiliar sounds, and historical unidentified acoustic phenomena have sometimes later been traced to marine life. A particularly instructive case involves the so-called “bio-duck” sound recorded in Southern Ocean waters. Research published in 2014 identified Antarctic minke whales as the source of that long-unexplained signal. That discovery does not establish that Antarctic minke whales produced the Soviet Quackers, especially given the different geography of many reports, but it demonstrates how a persistent and apparently mysterious underwater signal can eventually receive a biological identification.

Other possibilities include acoustically complex propagation through ocean layers, reflections, geological or environmental noise, known marine species perceived under unusual conditions, submarine or surface-vessel machinery, deliberate acoustic devices, and combinations of unrelated sources grouped under a common nickname. The surviving accounts may therefore not represent a single phenomenon. Similarity in sound or difficulty of identification is not sufficient to demonstrate that every reported “Quacker” had the same cause.

Modern UFO and USO literature has increasingly incorporated the Quackers into narratives concerning unidentified submerged objects. These versions sometimes describe intelligent craft maneuvering around Soviet submarines, testing naval defenses, communicating with crews, or moving at extraordinary speeds. Such interpretations go significantly beyond the strongest publicly available testimony. The original phenomenon, as presently documented, concerns unidentified underwater acoustic signals and interpretations of their apparent movement, not direct observation of confirmed physical craft.

The Soviet Navy “Quackers” should therefore be treated as a historically interesting but incompletely documented Cold War acoustic mystery. Named former Soviet naval officers have described unexplained sounds and institutional concern in considerable detail, giving the tradition more substance than an anonymous naval legend. What is presently missing is equally important: original sonar recordings, operational logs, contemporaneous incident reports, administrative orders creating an investigation program, scientific analyses, and a reliable event-by-event chronology. Until such records can be recovered or independently verified, the archive should distinguish the existence of retrospective Soviet naval testimony from later claims that submarines were demonstrably encountering intelligent or technologically extraordinary underwater objects.