While the British Government were able to throw financial resources and manpower at their code breaking and intercept facilities at the Bletchley Park facility, the Irish Government had a more low key approach.
The Radio Intercept Service was formed in 1940 as the Military struggled to listen to the growing number of stations and wavelengths across the spectrum. Broadcasts had to be monitored twenty four hours a day. Not only were they monitoring foreign broadcasts into Ireland, but local illegal radio stations and clandestine espionage stations operated by German spies in neutral Ireland.
There were twenty five civilians listeners none of them members of the defence forces or the Gardai but reporting to Military Intelligence with radio logs and signal information. These listeners came from all walks of life Architects, Insurance officials, drapers and even a clerk at Guinness’s brewery. Some of them operated homemade listening sets that allowed them to not only listen to medium wave and long wave but also the short wave bands. They were each assigned times and frequencies to listen to.
They detected coded messages being sent from the British to their own forces, German spies in Ireland, distress signals from torpedoed ships and Irish army broadcasts. It took some time for a list of safe stations that did not need further attention.
Some of the intelligence gathered on unlicensed wireless transmitters was garnered from the post office intercepting post and seizing QSL cards sent from radio operators to overseas ‘ham’ operators.
Suspect signals was often linked to local Garda reports from concerned citizens. This would be followed up by army intelligence investigation and then if nessessary raids conducted. Sometimes their were innocent explanations for ‘unidentified Morse code signals’ as perhaps a local electrical dynamo or cross signals.
They were able to identify both Allied and Axis broadcasts on normal stations when a Morse tone would be broadcast between programmes to inform spies to listen to their private transmitters for messages from their spy masters.
Commandant Sean Nelligan of the Irish Army commented ‘the magnitude of the task can however by gauged from the fact that it took the signal corps plus the PO Engineering Branch four to five months to locate a station that operated on a regular schedule, the wavelength having previously been made public.’ This was a reference to the IRA’s pirate radio station operated in 1939 from Ashgrove House in Rathgar.
If a suspect signal was detected and believed to be broadcasting within the state, the Military and Post Office had two detector vans at its disposal, something lacking in their 1939 search until one was borrowed from the British authorities.