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Eerie Port

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Eerie Port, on the northwest shore of the Great Cumbrae in the Firth of Clyde, was the site of one of the more unusual installations to form part of the Clyde's submarine defences during World War II, an acoustic listening post which listened to the underwater sounds in the approaches to the firth.

Listening post

The post was located in two single storey buildings near shore, one of which housed equipment intended to listen for, and detect the sound of any vessels attempting to penetrate the Cloch boom which stretched from Dunoon to Cloch Point, and protected the approach to the Firth of Clyde. Although not further described, the station must have been connected to an array of hydrophones (underwater microphones) which fed what appears to have been a huge, valve-based amplification system. Transistors were not invented until 1947, well after the war, and the equipment block has been described as having large ventilators, consistent with the need to dissipate significant amounts of waste heat, as would have been produced by an installation which utilised a large numbers of continuously running, valve-based amplifiers.

The second building served as an accommodation block, and is described as having had a small machine gun emplacement nearby, which was not evident during a later site survey.

Destruction by Challenge Anneka

Greycraigs Outdoor Centre, © http://www.geograph.org.uk/user/bill/
Greycraigs Outdoor Centre
© william craig

Some time between 1989 and 1995, the station was transformed into a residential holiday centre for deprived children. This development was carried out as one of the weekly challenges presented to Anneka Rice in the BBC television series, Challenge Anneka. Unfortunately, the format of the programme was such that the work involved was seldom carried out with any regard for the subject's history, as the presenter was given a limited time in which to complete the given task, usually 48 hours, and no cash or budget with which to complete it. Purchasing of labour and material was not allowed, and these had to be obtained through public appeals. With the shooting schedule of the programme dictating the availability of time, scant regard would be given to any remains of the listening post, if any, that might have survived in the old station building, which would have been stripped to make way for the new interior.

The station building has become the Greycraigs Outdoor Centre, Millport, Isle Of Cumbrae, and the Osprey Holiday & Conference Centre.

A report regarding the station was made in 1996, but this was completed after the redevelopment work had been carried out:

Two single storey buildings situated close to the shore at Port Eerie. These buildings comprised a listening post for the underwater defences in the Clyde. They were used for listening for any vessels which might be attempting to penetrate the boom defences crossing the preliminary barrier under the Firth of Clyde. In addition, the living quarters were in the large square blockhouse and a small machine gun emplacement for a lewis or bren gun was situated close by. The blockhouse with the listening equipment inside had large ventilators to allow the heat being created from the many electrical valves to escape. The valves were used to provide a link to the wires connecting under the Clyde to Toward Point in Cowal. The buildings have now been converted into a Outdoor Activity Centre for children and has been completely refurbished thus removing all of the internal wartime features.

Local reports

Local reports describe fixed anti-submarine defences in the Clyde, particularly in the area of Toward and the Great Cumbrae, as Hush-hush Units, and the description of the facilities installed at Eerie Point, further described as connecting under the Clyde to Toward Point may explain how the term came to be applied to them.

Initially, these were thought to have been references to Indicator Loop Station, similar to that a Ganavan, near Oban, but the name, other than as a reference to security (and therefore a little pointless), suggested something else may have involved, and this has now proven to be the case.

From the description of the installation at Eerie Port, there can be little doubt that the equipment was used to carry out acoustic monitoring of the Firth of Clyde using a large number of sensitive microphones, or hydrophones, laid out on the seabed between the Great Cumbrae and Toward. From local reports, the most likely location of the Toward end of the line would have been Oakbank House, said to have been first requisitioned as accommodation for WRENs, and later to have housed a station referred to as a Hush-hush. Local accounts tell of personnel taking small boats out into the firth, where they dropped grenades into the water. This would have been entirely consistent with the operation of such a facility, as the acoustic pulse generated by the resultant explosion could have been used to calibrate the underwater hydrophone array.

Given the level technology in the 1940s, and the lack of modern microprocessor-based adaptive digital filtering and analysis techniques now available, the station operators of such a facility would have been plagued by the effects of ambient noise, which would have arisen naturally from sea, and the effect of waves breaking on the surface and shore; the movement of all the legitimate vessels in and on the Firth of Clyde, and those many miles away, because sound travels considerably further in water than air; the din from shipyards on the Clyde; the sound of aircraft (propellers); local traffic, and even people on the shoreside roads. The description of the stations as Hush-hush units is much more likely to have arisen from the staff and operators, as they fought to silence the unwanted sound signals which interfered with their targets, than any clandestine references, but the double meaning makes for a better story.

No information has come to light about the technical operation of any stations such as that located at Eerie Port, although the US Navy created a modern system based on a similar concept, known as the US Navy Sound Surveillance System (SOSUS), listed in the Links below.

Note that a further station identified as having been associated with Ant-Submarine operations has also been described at Ardhallow. Unfortunately, subsequent re-routing of the local road has erased all traces of this site.


At the end of World War II, relations between the US and the Soviet Union were already cooling, and America considered itself to be vulnerable to Soviet ballistic missile submarine attack. In an effort to counter this potential nuclear threat from the east, the US Navy began to develop a system of underwater listening stations that would eventually become one of the most effective oceanic monitoring systems ever created.

Development of the Sound Surveillance System (SOSUS) began in 1949, as a tactical, long-range system intended to counter the emerging Soviet submarine threat. Most of the Soviet submarines were still operating, diesel engines, making then easy to track. The system worked by monitoring the SOFAR channel, a horizontal layer of ocean water through which sound travels at its slowest speed, which allows low frequency sounds, such as the knocking of a diesel engine, to travel hundreds of miles before dissipating.

Warmer waters near the ocean surface allow sound to travel relatively quickly. At greater depths, where the water become cooler, the speed of sound decreases toward a minimum, and pressure effects take over, the speed of sound begins to increase again, as depth to increases. The deep sound channel is found at the depth where the sound velocity is a minimum. Because sound tends to bend away from regions of higher sound velocity, a wave directed upwards from the sound channel axis will be refracted back down again, and a wave directed downwards will be bent upwards. The result it that sound paths from sources in the deep sound channel weave back and forth across the channel axis (because they become trapped in a deep ocean layer away from the surface or bottom) and can travel long distances with minimum attenuation. In addition, propagation mechanisms exist which bring near-surface sound down to the depth of the sound channel, so those signals also become trapped and traverse long distances with minimal loss. The sound channel axis is normally found at a depth of several thousand feet (depending on thermal conditions), and because of the unusually warm waters of the Gulf Stream and Sargasso Sea, it is deeper in the Atlantic than in the Pacific.

By setting up multiple listening posts—arrays of hydrophones strung along lengths of cabling, at strategic choke points like the GIUK gap (the channels between Greenland, Iceland, and the UK), the US Navy could triangulate, and track the locations of otherwise invisible deep-diving Soviet submarines. After three years of intensive development, the US Navy installed its first SOSUS array off the coast of Eleuthera, a small island in the Bahamas, in 1952. The array comprised a 1,000 foot long string of 40 hydrophones at 240 fathoms (1,440 feet), and spotted US submarines in the area so well that the US Navy immediately expanded the program to include the entirety of the eastern seaboard as well as the west coast and Hawaii in 1954.

Before the signals from the hydrophones could be used, they had to be transmitted back to onshore naval facilities. Each signal was processed so that it only measured a narrow band of frequency, which largely eliminated interference from background ocean noise and aided naval analysts in discerning the tell-tale acoustic signatures of the Soviets Submarines.

Since then, SOSUS was eventually supplemented by surface-based listening posts such as the Surveillance Towed Array Sensor System (SURTASS), and was later integrated into the larger Integrated Undersea Surveillance System (IUSS). While the abrupt end of the Cold War reduced the need for such a system, growing concerns of China's rising naval power and Russia's renewed aggression have seen the US Navy's Space and Naval Warfare Systems Command (SPAWAR) proposing commercial ventures and defence contractors alike, to create a new generation of listening stations.


1 Information from Defence of Britain Project recording forms, V Bickers, 1996.

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