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Thread: Mersey H18 HAA Site

  1. #1
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    Default Mersey H18 HAA Site

    I've been past here on the M56, thousands of times, and never taken a blind bit of notice of this, but I spotted it on Google Earth:



    From GE, it looks intact, and it is. The owners use it as a commercial site, but it has been left as is. Vistors are welcome, provided you ask.

    It was one of two AA Sites that defended the Frodsham Railway Viaduct, easily seen across the Weaver from the M56 viaduct.

    The reason for the military importance, was that just up the railway line was ROF Dunham-on-the-Hill, which was the primary warehouse and distribution centre for explosives shipped into the Mersey, they were then sent by rail to other "Filling" ROF's. Hence it's importance.

    It was a pretty standard 3.75 inch set-up, with 4 AA guns (and curiously a 5th, but with no enclosure), a control building for the range finder and height finder, and a generator building for power.

    The approach road, it still has the original fence posts:



    One of the four gun enclosures, unusually with extra ammunition storage on the outside, which suggests that it was a late build (D-o-t-H opened in 1942):



    Ammunition locker with steel doors:



    Without doors, showing original wooden supports for shells:



    Gun holdfast, and channel for control cables:



    Ramp down to control building:



    General view of control building with soft asphalt roof (no sparks):





    Inside - not a lot:



    eeeek !





    Generator building:





    And an arty farty sunset:


  2. #2
    Senior Member PETERTHEEATER's Avatar
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    Default Re: Mersey H18 HAA Site

    Re Image 8, I'm durned if I can remember what it was called but the stuff on the roof was tar impregnated felt or similar to rain proof the slab roof. You can see how it has been folded over the edges and stuck down.

    Nice to see an intact site. Like you I have driven past it many times but knowing it was there and not able to detour (Danger - wife in car!).

    Now you have shown us. Thanks.

    I see that you have shown it with North to the bottom of the image to deceive the enemy! (Just to the right of Sutton Weaver PNK)
    Last edited by PETERTHEEATER; 08-08-2009 at 06:31.

  3. #3
    SuperMod Peter Kirk's Avatar
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    Default Re: Mersey H18 HAA Site

    Another informative post. I had a look around and found these of the are

    Taken early post war I assume with the radar mat (does it have a proper name) still in place.


    I think this was taken slightly later maybe into the 50s.


    An early 1970s shot


    The paths around the emplacements seem to have chaned post war an two emplacenments are gone by 1970.
    Last edited by Peter Kirk; 08-08-2009 at 09:33.

  4. #4
    Senior Member PETERTHEEATER's Avatar
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    Default Re: Mersey H18 HAA Site

    Radar Mat? You've got me there. Something new to me.

    I assume that it is metal mesh laid on the ground to create a 'plane'.

    Perhaps one of a RDF experts can enlighten us with technical details?

  5. #5
    tigger
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    Default Re: Mersey H18 HAA Site

    The matting provides an efficient ground plane for the RADAR transmitter. The earth works as a ground plane but isn't very efficient (not conductive enough).

  6. #6
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    Default Re: Mersey H18 HAA Site

    It was to provide an artificial horizon for the early "Gun Laying" radars, and was usually known as a "GL" mat. I've seen a comment that they used up all the chicken wire in the country.

    They were usually well off the ground, and their location is frequently (easily!) recognised because they had a "GL" concrete ramp which was to raise the radar vehicle above the mat.

    Here is an example at Gloucester Farm (Blyth), with an access road taking an octagonal path around it. Also shows different types of revetments on the same site.





    This example had "store" rooms underneath the mat.



    I'll do a separate thread on Gloucester Farm to illustrate better.

    This example (Brimstage / Storeton) on the Wirral shows the ramp.


  7. #7
    Senior Member PETERTHEEATER's Avatar
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    Default Re: Mersey H18 HAA Site

    Ground plane I understand. I use a VHF receiver and one of my aerials has ground plane elements. What I failed to remember is that the RDF frequencies in those day were much longer than modern radars even when the centimetric radars came into use so a 'ground plane' was relevant. (or have I got it all wrong?)

  8. #8
    tigger
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    Default Re: Mersey H18 HAA Site

    Only the receiver cabin was raised above the artificial ground as the returned signals tended to be absorbed unevenly by the irregularity (both topography and conductivity) of the actual 'soil' surface.

    I beleive the quote about using all of the countrys stock of chicken wire was attributed to General Pile but there is no firm evidence that all of the wire was in fact used. The matting wasn't installed initially but was added as a part of the improvements when the 'Elevation Finding' attachment was added.

    related but at a slight tangent.....Does anyone know at what point 'GL' changed from 'Ground Locating' (which was the actual expanded form in the official designation of the RADAR) to 'Gun Laying' (which seems to be the popular version)? Perhaps when the matting and the EF attachment were added.

  9. #9
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    Default Re: Mersey H18 HAA Site

    Anyone care to comment on the "store rooms" beneath the GL mat on the Gloucester Farm photo above?

    I haven't seen them anywhere else.

    The reference to chicken wire is in Pile's book. I read it last night.

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