Submarines, sonar and spooks
Are submarines vulnerable to an effect science refuses to believe in, asks DAVID HAMBLING
Weird science involves obscure unexplained phenomena with little significance in the wider world; but occasionally it might have strategic significance. The strange effect known as ‘NIDAR’ is a case in point.
During WWII, early radar operators saw peculiar traces on their screens, vast but vague objects, typically about 500m (1,640ft) across, moving slowly at an altitude of a few hundred metres. These ‘spooks’ appeared and disappeared unpredictably. There were no ships or aircraft to account for the radar returns. The mystery deepened when the traces were found to be following the position of submerged submarines.
This seems impossible: radar waves do not penetrate water. A surfaced submarine, or even one with just its periscope above the water, might show up on radar, and radar proved very effective at spotting submarines at the surface in the dark and in bad weather. But a submerged sub is as invisible to radar as an underground pipe is to the naked eye. In spite of this impossibility, there were many anecdotal reports of radar operators seeing ‘spooks’ over submarines, mainly on gunnery radar. The spooks could be seen from up to 30km (18 miles) away, and appeared to follow the sub as it moved. Reports came from everywhere, from the Gulf of Mexico to the Straits of Gibraltar, and from US Navy forces in New England and Virginia. The effect was even used to supplement sonar tracks and help follow subs in exercises. Incredibly, subs at depths as great as 200m (656ft) appeared as radar spooks.
The spooks were not consistent. Submarines were not always accompanied by spooks, and they could not be demonstrated to order. Given that the spooks should not be there at all, scientists regarded the reports as mistaken and therefore worthless. It was a classic case of Fort’s ‘Damned Data’ – observations that contradicted known science and were ignored as a result. Submarine spooks were put in the same class as Unidentified Flying Objects, some of which were artefacts caused by glitches in early radar systems (see FT195:36-37). Neither was taken seriously.
However, enough reports piled up that even the US Navy could no longer entirely ignore them. An official programme of experimental investigation, known as Project NIDAR, was carried out between 1956 and 1959 by the Atlantic Destroyer Force. In one test the destroyer USS
Glennon successfully used its gunnery radar to follow the submarine USS Crevalle (pictured above) while it was submerged at a depth of 50m (164ft) and moving at 3km/h (1.9mph). The tracking continued for an hour and a half, although the radar spook wavered and sometimes seemed to split into several different clouds. “It is hard to imagine how a submerged submarine can give rise to an effect one or two thousand feet above the surface,” noted Merrill Skolnik, a leading US radar scientist, in an official report on Project NIDAR. “It is indeed understandable why there might be scepticism. Nevertheless, it is an experimental observation reported on many occasions.”
The term NIDAR came from Nuclear Induction Detection and Ranging (in imitation of RADAR and SONAR), because researchers thought it might be caused by a mysterious nuclear induction effect in the atmosphere. However, by 1958 an official report on Nonacoustic Methods for the Detection of Submarines noted that: “Everybody admits – even the inventor of the word by now – that nuclear induction spin echoes have nothing to do with these radar returns.” A later theory suggested spooks were related to clear air turbulence. This was many years after Project NIDAR, when more was known of atmospheric effects on radar. Warm air is lighter than cold, and so tends to rise. When the air at sea level is heated by the Sun, rising bubbles of warm air called convective cells form. These may be several hundred metres across and show up as a faint cloud on radar, just like the radar spooks.
The new theory held that surface turbulence from the submarine mixed lighter moist air with heavier dry air and produced a similar rising bubble of air that would be visible as a radar spook. While this might work for a sub close to the surface, a submarine at 100m (328ft) produces a bow wave less than 1cm high, hardly enough to generate a spook.
The Navy Research Laboratory researchers were not convinced and concluded that the radar was locking on to waves, rather than anything in the air. In 1959, NIDAR became Project Cutwater, concentrating on developing advanced radar to detect the submarines bow waves. NIDAR test data was ignored, and Cutwater gradually moved to detecting periscopes and snorkels rather than wakes. This avoided unexplained phenomena or weird science. In fact the new radar worked by cancelling out all background ‘noise’ – including the spooks.
Skolnik, who had been involved in the original tests, still believed that NIDAR had detected something. He carried out another analysis decades later, in a 1975 Navy report which was also apparently ignored (and classified). Skolnik wrote yet another report in 1996 which is still classified, but which appears to repeat the same theme.
The Russians, who lacked good sonar and needed other ways of tracking subs, seized on the NIDAR effect. Soviet antisubmarine vessels had notably large radar antenna. Skolnik noted that these would be ideal for spook spotting, and in the 1960s some claimed the radar could detect subs. These claims were dismissed by Western analysts. The technology has no doubt progressed since then.
We still rely on submarines for our strategic deterrent. The Royal Navy proudly (and uncheckably) claims that no Trident submarine has ever been detected while out on patrol, and an enormous effort is under way to ensure that the Dreadnought subs replacing them will be undetectable by sonar. But if researchers do not believe in submarine-generated UFOs they will not find out how to prevent them – and with a radar spook hovering above them giving away their position, any submarine may be a sitting duck.
The spooks could be seen from 18 miles away and followed the sub as it moved