Acoustic Mirror at Kilnsea

[Nancy Bunting]

I'm hoping the knowledgeable people of this website might be able to help me out. This has to do with research on JRR Tolkien who was posted in Yorkshire after recuperating from recurrent trench fever acquired in France during the Somme offensive in 1916.

The sticking point is WHO was in command of the acoustic mirror at Kilnsea? We believe it has to be the Royal Garrison Artillery at Spurn Point but we don't have documentation. I will add some relevant paragraphs:

Lt. Tolkien’s transfer from the Lancashire Fusiliers to 9^th Battalion, the Royal Defence Corps or RDC, headquartered at Easington, would have been due to practical military considerations. This new posting meant that, again, Lt. Tolkien and Tolkien’s RDC Battalion were reporting to the Humber Garrison. The RDC was comprised of Category B (previously Class II) infantrymen unfit or too old for General Service but sufficiently fit for Home Service (Mitchison 60), generally men of ages 41 to 60. This RDC Battalion was a coastal defence unit posted along the sea-wall by Kilnsea, watching for enemy activity off the coast and in the air. The Battalion may have had a Signals Company attached, drawn from the East Riding Volunteers (ERV) (Mitchison 396). However, they are not likely to have had a trained and experienced Signals Officer.

Watching for enemy activity encompassed a range of responsibilities for the RDC because the estuary of the Humber was a location of significant activity for British navy, army and flying corps. British aircraft flew over Spurn Point daily on their way from their base at Howden, forty miles to the west, to escort convoys or to fly anti-submarine patrol in the North Sea (Firth 16). Returning at dusk was particularly dangerous because from a distance these British aircraft, even if smaller, often looked very much like the German ones.[1] In addition, after February 1, 1917, Germany resumed unrestricted submarine warfare. This included German submarines constantly laying mines along the North Sea coast including the approaches to the busy port of Hull on the Humber. In response, a ‘War Channel’, one mile wide and 540 miles long, marked by buoys, was established to protect naval and merchant ship convoys. Converted trawlers out of Hull constantly swept this channel because mines often escaped from their undersea moorings.[2] Men of the RDC would be watching for these wayward mines as well as checking the identification of all vessels using signal lamps, wireless transmissions, and even possibly pigeons.[3] These observers would have also carefully distinguished German from British aircraft.

The RDC did not man the Kilnsea acoustic mirror, a forerunner of the later radar network, even though one would think that would be part of the network of coastal surveillance. This was under the jurisdiction of the Royal Garrison Artillery who supplied an observation officer who could understand the somewhat complicated calculations required to identify the necessary coordinates and who was likely to have the acute hearing needed for this station (*).[4]  The acoustic mirror was only manned when the Humber Garrison was notified by a ‘Field-Marshal’s Warning’ from the Horse Guards in London of the approach of enemy airships.[5] The crucial information from the coordinates of the acoustic mirror was passed to a cooperating battery of searchlights and urgently notified all other anti-aircraft units of the Humber Garrison and Horse Guards in London.[6] On March 12, 1918, during Lt. Tolkien’s time with the RDC, a Field-Marshal’s Warning arrived before dusk because five ‘Height Climbers’ had left for England (Hamill-Keays “Zeppelins” *).

RDC did NOT have the competence to read the azimuth etc. that was needed from the acoustic mirror. When the Humber Garrison got the notification of the 'Field-Marshall warning' then they sent an officer out to the mirror. The RDC would not have been receiving this warning. It seems that the RGA would have to be the unit responsible for monitoring the acoustic mirror. Can anyone help us with documentation? We seem to have hit a wall. Seamus has put in an inquiry to the Royal Artillery but has not gotten a response.

I need to make if very clear that even though Tolkien was an experienced and trained Signals officer (we know he had training for and used a Fullerphone in the fall of 1916), he was NOT in the loop for the acoustic mirror. That was in a different jurisdiction.

Any thoughts, suggestions, or help would be greatly appreciated.

Yours,

nabindigo1

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[1]. Four of the airships stationed at Howden were large and impressive ‘Parsevals’ of German design. Good communications with the defence forces was even more essential for these (Mowthorpe Appendix D).  

[2] Three hundred Hull trawlers were used as minesweepers on Admiralty service during the Great War. Of these,

 sixty-one were lost, many to mines (“Kingston-upon-Hull War Memorial. 1914-1918: Hull’s Sea War,”  last viewed

on 6/17/2023. https://www.ww1hull.com/the-war-afloat/.

[3] “The First World War, East Sussex: Feathered Warriors.” http://www.eastsussexww1.org.uk/feathered-warriors/index.html and The birds were vital to the army and navy too, as they were used to communicate between Royal Navy ships that did not have wireless telegraph systems. https://www.nationalarchives.gov.uk/first-world-war/home-front-stories/policing-pigeons/, last viewed on 6/13/2023.

[4] For more information see: “HERITAGEGATEWAY: Historic England Research Records: Spurn Point Military Defences,” last viewed on  6/19/23. https://www.heritagegateway.org.uk/Gateway/Results_Single.aspx?uid=916014&resourceID=19191#:~:text=Summary%20%3A%20Spurn%20Point%20Battery%20was,Battery%20(see%20UID%20916096).

[5] ‘Room 40’, the code name of the cryptoanalysis section of the British Admiralty, had obtained copies of the

German Navy’s codebooks and could deduce from enemy wireless transmissions (WT) when an airship was

departing for England (Jones III 118). Every German airship used a radio navigation method, and this signal was

picked up by radio direction-finding (RDF) stations in Germany, but also in Britan (Phimester 9.1.4) The Germans

never knew that the British developed RDF to track Zeppelins, (Beesley).

[6].  Assuming an airship was approaching at 20,000 feet and flying at 60 mph at 6.5 miles horizontal, it would have been nearly ten minutes before it was head by land-based monitors (Hamill-Keays, “Zeppelins” *).

[exXIX]

I too have researched these sound mirrors but in the Tees area. The warning for the North East was from constantly manned installations at Boulby, Redcar, Hartlepool and Sunderland. Warnings were given to the Sector Control Point (in Redcar's case the RNAS Station at Redcar) which provided about 20mins warning, which was just enough to get an aircraft aloft to intercept as it crossed the coast, weather permitting of course.The warning also went to the local searchlight batteries around Teesmouth and Boulby. I believe Hartlepool's was the RFC Station at West Hartlepool (who successfully plotted and directed an aeroplane which shot down the offending Zeppelin). There is an article on it on my blog if you would like to use any of the information, http://www.talesfrommyshed.wordpress.com  some of the details I got from War Office Instructions on Archive.org and some is conjecture that makes logical sense, as well as the Hartlepool Mail website who ran several articles in 2014, also Tees Archeology website...

 

 

Edited 1 July , 2023 by exXIX

[Major Claves]

The first line of defence against German airships was formed by the Marconi tracking stations that listened in to the WT exchanges between an airship and triangulation bases in Germany that were able to inform the commander of which square of a plotting map his airship was in. The Admiralty's Room 40, precursor of GCHQ, that  possessed a copy of the German Navy code book,  listening to German 'departure' WT, knew when an airship had lifted off and notified the Home Army HQ. This HQ in London was also passed the Marconi tracking coordinates.  The defenders thus knew when an airship attack was on its way. At an appropriate time, when the likely target had been deduced,  a warning was sent from London to the defences the airship was approaching.

  The second line of defence was the anti-aircraft artillery of the RGA on the coast of eastern England.  In all cases, it was essential that the guns were laid with the correct polar coordinates by the gunners.. Before advanced models of Zepplins were introduced, the noise from their engines gave a clue from which direction the airship was approaching. After the first 'Silent Raid' when the attacking airships came in at 20,000 feet unheard by the defenders, it was realised there was a need to develop a method of amplifying the engine noise. This led to the creation of the acoustic/sound mirrors. These paraboloid concrete structures were hit by the sound waves of the incoming airship, particular areas of the concavity receiving a higher intensity. A two axis alignment bar mounted on a pole in front of the mirror carried a stethoscopic horn connected to typical medical stethoscope earpieces in the ears of the operator.  The operator moved the alignment bar and the horn over the surface of the mirrror until a maximum result was obtained. The azimuth and elevation angles of the alignment bar were passed to the nearby searchlight battery and the AAA. This was part of more accurate gun-laying and was in the province of the gunners.

There is an excellent US video with photos of the alignment bar, horm and earpieces at https://www.pbslearningmedia.org/resource/nvzt-sci-locatesound/locating-zeppelins-by-sound/#.XkVZ6iPgqUk

Major Claves RA(Rtd)