In my view, any recollection of oceanographer Walter Munk’s long string of accomplishments (see C. Wunsch Nature 567, 176; 2019) should note that these were marred by one huge, ecologically risky experiment.

In January 1991, Munk ran a feasibility test of acoustic tomography near Heard Island in the Indian Ocean, whence sound waves would propagate through all the world’s oceans (A. Baggeroer and W. Munk Phys. Today 45, 22–30; 1992). The plan was to project sound horizontally at an intensity of 221 decibels, at a depth of 100 metres, where the SOFAR acoustic channel would act as a sonic wave guide. The sound would be pulsed, with one hour on and two hours off.

Because of concerns about the effects of this unprecedented level of acoustic energy on marine mammals worldwide, the project needed a permit for “limited harassment” of whales (J. Cohen Science 252, 912–914; 1991). Such was Munk’s influence that the permit, requested from the US National Oceanic and Atmospheric Administration on 15 October 1990, was granted on 7 December and revised 3 days later to increase the number of animals that could be harassed from 10 cetaceans to 234,200, and from 100 pinnipeds to 115,000.

These ocean creatures were intermittently subjected to this excessively loud sound source for five days (subsequent studies based on the results of this test aimed to reduce the sound intensity by 20 dB). Munk’s hasty and scientifically naive experiment was one of the largest ever conducted on the world.