Admiralty M-N Scheme Submarine Detection Device

[Captain Jack]

So on the wiki page for the Admiralty M-N scheme towers there is a throw-away reference to them being equipped with a device to magnetically detect the presence of a submarine. This piqued my interest as I've never seen anything else about this device and as far as I can tell submarine detection in WW1 was limited to hydrophones though both the French and British had prototype sonar (asdic) systems by 1918. I followed the source cited by wikipedia and it lead me to a website about Guy Maunsell of WWII Maunsell Sea Forts fame. This website had the following to say about the devices:

Gibb, fellow Admiralty employee T.G. Menzies and electrical engineer Colonel William McLellan (1874-1934) had worked together to invent a way of locating submarines by means of a galvanometer. The range of their devices was only 3-5km, so a line of towers would be needed. McLellan was a founding partner of the consultancy Merz & McLellan, which he and Charles Merz (1874-1940) set up in 1902 (it became part of Parsons Brinckerhoff in 1995).

Not particularly helpful. So does anyone know anything about these submarine detectors? Can we guess at how effective they would have been? Might it have been possible to utilize the detectors on a escort ship, though it would require degaussing the vessel in question no?

While we're at it feel free to discuss the M-N towers in general. Personally, I think the towers would have worked at keeping German submarines out of the Channel but I doubt they would have been enough of an improvement over the existing Barrage to warrant the expense. What say you?

Admiralty M-N Scheme: http://en.wikipedia.org/wiki/Admiralty_M-N_Scheme#cite_note-4

wiki citation (reference 4):http://www.engineering-timelines.com/who/Maunsell_G/maunsellGuy3.asp

 

[Andy42]

Coastal defences in later WW1 and in WW2 used induction loops to detect subs and other vessels passing the defences. The port defence mine barrier could then be electrically switched on.

The detection system was based on cable loops laid on the sea bed that detected the electrical change in the applied field.

However that sort of thing only works for relatively narrow estuaries, river mouths and so on, not for long distances such as the channel or the straits of Gibraltar. Depths are too much for one thing - estuaries are shallow.

Not a practical device for warship use, even today. Aircraft are a different matter.

In WW2 detection loops were applied to Wellington bombers, and later to the Catalina flying boat. The detection range was so short that the planes had to be fitted with rocket-braked depth charges that would fall pretty much vertically on receipt of a signal.

Not much success was had with these, but the Gibraltar gap was patrolled by the Catalinas on a fixed racetrack pattern, and from what I recall reading years ago one sub may have been engaged by them.