'Consol' was the British name for the German 'Sonne' system developed pre WW2. It was a general navigation system but primarily used in WW2 by the German U boats. There were three staions origianlly. One in Spain, one in Quimper, France and one in Stavanger, Norway. It transmitted a series of dots and dashes on 300khz and the beauty of it was that a nav fix could be made by anyone with a radio that could receive that frequency. So an ADF could be tuned and a count done.
To use it, you listened to the series of dots and waited for the dash. The dash related to which 'radial' you were on. You noted what time you got the dash and looked up the time split from the start of the signal on the Consol chart. A 3 position line fix could take some time as I seem to remember that one count sequence could take about a minute.
One of the reasons why it didn't get blown up was that the allies used it as well, although I seem to remember reading that some selective jamming and spoofing took place. It was well known by the allies as it was a commercial facility pre war.
After WW2, it was maintained and additional stations were added. One in Ballykelly, Northern Ireland was blown up by the IRA who thought it was a listening station.
I seem to remember the Stavanger station being in existance up to 1990.