In the course of the last thirty years, several attempts were made to find extraterrestrial neutrino sources. Detectors were installed in deep mines and tunnels to provide adequate shielding against the muons produced by the primary cosmic radiation in the atmosphere that are indistinguishable from muons resulting from neutrino reactions. As an additional criterion, it was required that the muons traverse the detector from below, in an upward direction, emerging so to say from the interior of the earth. Since muons cannot traverse the earth it is evident that upward moving muons must result from neutrino reactions taking place inside the earth, underneath the detector.

All attempts failed, chiefly because of the inadequate size of the detectors. (We ignore the detection of the very low energy neutrinos from the sun and the supernova 1987-A, as they are of no concern to this paper. The energy of these is about one million times less than those with which we are concerned.) Our calculations and estimations have shown that a detector of the order of 1 km^3 would be needed in order to work out a full sky neutrino source survey. In view of the practical limitations imposed on the size of underground detectors, the successful search for extraterrestrial neutrino sources might have seemed hopeless.

But in the early sixties M. A. Markov, a member of the former Soviet Academy of Sciences, proposed to use the ocean as a muon and neutrino detector. He suggested distributing highly sensitive optical sensors (electronic eyes) at great depth in the ocean in the form of a three-dimensional matrix, such that they could view a huge volume of water (figure 1). Charged particles, such as high energy muons, that move at the velocity of light in a refractive medium such as glass, water, air, etc. (the velocity of light in water is approximately 67% of that in vacuum), produce a trail of light along their trajectory called Cherenkov radiation. From the signals recorded by the optical sensors (time and amplitude) the trajectory of a high energy muon in the ocean can thus be reconstructed very accurately with the aid of a computer, and consequently that of its parent neutrino.

The water masses above the sensors serve to shield the detector volume from the undesired cosmic radiation and absorb the interfering daylight. The nuclei of the hydrogen and oxygen atoms that constitute the water are the occasional collision partners of the neutrinos, from where the detectable muons emerge.

This brilliant concept which uses the water masses of the ocean as a multipurpose medium aroused great interest among many scientists. It brought the prospects of building a Deep Underwater Muon And Neutrino Detector - DUMAND - into the realm of reality. However, technological problems were evident, which led some of our less ingenious colleagues to label such an endeavor that now approaches completion as pure utopia.