In 1991, the islands were the location for the Heard Island feasibility test, an experiment in very long-distance transmission of low frequency sound through the ocean. The US Navy vessels and were used to transmit signals which could be detected as far away as both ocean coasts of the US and Canada. The "Cory Chouest" was chosen because of its central moon pool and because it was already equipped with an array of low frequency transmitters. A phase-modulated 57 Hz signal was used. The experiment was successful and demonstrated that such sound waves could travel as far as the antipodes. Planned transmissions had been for ten days, although owing to the bad weather conditions and the high failure rate of the transmitter elements, used at a frequency below their design frequency, the transmissions were terminated on the sixth day, when only two of the original ten transducers were still working.