Overwater navigation for airplanes used to be a tad more challenging in the days before GPS and Inertial Navigation Systems.  Out in the open ocean, there are no landmarks from which to triangulate a position.  They had logged data of headings, airspeed, and calculated wind drift; the sextant with tables of data; and a guy whose job it was to keep track of the aircraft's position.  But, what if you could artificially create triangulation data?  If you could measure the bearing from stations in Norway, France, and Spain, then you can pinpoint your location in the ocean with great accuracy.

One thing WWII Germany had was an abundance of scientists working on military problems like this.  One of these scientists, Dr. Ernst Kramar, came up with improvements to previous radio navigation systems and created the transmission system he called Sonne [German for sun].  The British found out about this system, and found it useful.  Instead of destroying the transmitters, they created their own charts for use by the Coastal Command bombers who were out hunting U-boats,  They called their system Consol [By the sun], using the German transmitters themselves.  Therefore, Sonne/Consol has the almost distinction of being a weapons guidance system used by both sides in a war.  It was even rumored that when the Germans were unable to repair one of the broken transmissio stations in "neutral" Spain, the British actually sent parts to fix it.  After the war, Consol became one of the standard ICAO navigation systems, with additional transmitters being built in the UK, US, and USSR.



British Consol chart from 1946:





Here's some more technical explanation of the system:


"This system was installed in Norway, France and Spain as a navaid for German aircraft flying the circuitous route over the Atlantic between France and Norway, and their U-boats. It is an example of a 'collapsed' hyperbolic system wherein the baseline between the transmitting aerials is made so short that the hyperbolae degenerate into radials at a very short distance and the system becomes a bearing system rather than a hyperbolic one.

Sonne/Consol used three aerials spaced on a line 1.5 miles long, or about three wavelengths at the operating frequency of 300 kHz. An identical signal was fed to all three aerials but at one outer aerial, it was delayed by 90 degrees of phase while at the other outer aerial it is advanced by 90 degrees. Multiple lobes with deep nulls between them were produced by the interaction of the three aerials. By steadily changing the phase shift in the two outer aerials so that it interchanged every 30 seconds, these lobes were caused to sweep. They were also switched at a very much faster rate in synchronism with a Morse pattern of dots and dashes, the effect being that each lobe carried only either dots or dashes and was replaced by its complement over the 30 second period.

The navigator only needed  an ordinary radio receiver tunable to 300 kHz in order to use the system.. He heard a series of dots slowly merging into a steady tone and then becoming a series of dashes (or -dashes becoming dots). He simply had to count how many dots or dashes he could hear before the steady tone and then plot his position line on a suitably overprinted map. There were multiple ambiguities in the system since there was no inherent way of distinguishing between one lobe and another. At its narrowest each lobe, it was only about 7.5 degrees wide. They were resolved either by approximate knowledge of position or by taking a loop bearing on the station. For this purpose, a steady tone was transmitted for a few seconds before each sweep, from the central aerial only. One station did not provide a fix, of course, but it was a very useful system requiring little expertise to use and only simple equipment."

http://www.ea1ddo.es/consol7.html



Other references for further reading:

http://www.jproc.ca/hyperbolic/consol.html

http://www.vectorsite.net/ttwiz_10.html#m1

http://www.radarpages.co.uk/mob/navaids/consol/consol1.htm

https://en.wikipedia.org/wiki/Sonne_(navigation)

Very cool. Much easier than waiting til dark to find out where you are.

Fascinating problem.  You've become dependent on the enemy's navigation system, one of their transmitters is down, and your ground forces have cut off their supply of spare parts.  You navigate the political waters, supply your enemy's navigational system with spare parts, and avoid being labeled a traitor to the Crown.