Report - - Black Down Starfish Decoy Site, near Cheddar, Somerset - April 2015 | Military Sites | 28DaysLater.co.uk

Report - Black Down Starfish Decoy Site, near Cheddar, Somerset - April 2015

Bertie Bollockbrains

There is no pain
Regular User
This report is about the starfish decoy site that was on Black Down during World War Two. Starfish sites were night-time decoy sites, usually built a couple of miles away from the real target, designed to confuse German bombers. Remember this is before the days of GPS and navigation would had been by looking out of the window with a map balanced on the lap. Starfish sites simulated burning cities and caused the Germans to drop bombs over the countryside.The name starfish comes from the military designation for such sites - SF (which actually means special fire). They consisted of elaborate light arrays and fires, controlled from a nearby bunker and laid out to simulate a fire-bombed town. By the end of the war there were 237 decoys protecting 81 towns and cities around the country. Starfish sites did attract the attention of enemy bombers; one estimate is that around 968 tons of ordnance was dropped on the decoys (reference: Fields of Deception: Britain's Bombing Decoys of World War II by Collin Dobinson). Very little now survives of any of these decoys, most having been cleared after the war.


The diversionary fire decoy at Black Down is one of only a very few to survive following the systematic clearing of such sites in the immediate years subsequent to the end of World War II. The site also encompasses the rare survival of World War II anti-aircraft landing obstructions in the form of mounds and cairns, this system being particularly visible from the air. These were constructed as part of a national programme in which all potential landing grounds were obstructed.

The Black Down bombing decoy was constructed in the early years of World War II as part of the defences of the city of Bristol against German air raid attacks. The aircraft landing obstructions were built as part of a national programme of anti-invasion measures. The site lies on Black Down at the western end of the Mendip Hills some 25km south west of the centre of Bristol. The decoy sites on Black Down were intended to replicate the lighting patterns for the centre of Bristol and the position of main railway depots when viewed from the air.

Surviving are two control buildings from which both the lighting and fire decoys were triggered. These stand on the southern boundary of the decoy site about 1.5km apart. Both are of the standard design for a control building or bunker being earth-banked and resting on a concrete raft 9m in length. Comprising two rooms, they are constructed of 0.35m thick brickwork with an outer blast-wall protecting the single entrance. The operations room would have contained a stove, switchgear, and other communications equipment; the other room would have housed the power generators. The westernmost control building at Black Down stands complete with its earth-banking and it retains a stove base in one room and three generator bases in the engine room together with some ducting. The easternmost control building also stands complete with its earth banking. It too retains a stove base in the operations room and additionally has traces of original paint on the walls - white with a black dado at waist height and green below. The engine room has bases for three generators with lagged pipes surviving in places into the outer walls. A third control bunker lies about a mile to the south of Black Down within a farm and is included in this report.

Crossing the area utilised for the decoys on Black Down are lines of mounds or cairns set up to prevent airborne landings on this relatively flat and unwooded area of the West Mendips. The grid of obstructions comprises three parallel WSW-ENE alignments each over 1km in length with one nearer to 1.75km in length, and twelve shorter lines running roughly at right angles to the three main lines. The earth mounds vary between 0.9m-1.3m high by 2.5m-3m wide and they are generally spaced at intervals of 8.5m-11.5m.

The Visit

A beautiful unseasonal bright sunny day and following a steep climb (for Black Down is the highest peak in the Mendip Hills) I reached the first Control Bunker. Sadly this was sealed up, but fascinating still:


Boooo who put this there?


The main entrance (gated and locked) is protected by a blast wall


In an adjoining field I saw a small bunker. Climbing a couple of barbed-wire fences I made my way in full view of the farmhouse. This was sealed too.


I made my way to the east control bunker, and yay it was open



Definitely a more upmarket middle-class bunker - check out this drainpipe:




And the three concrete bases used to house the generators in the generator room. Not shown in the photo are 3 30cm diameter holes in the wall which would had held ventilation pipes.


Overview of the control bunker:


Next I climbed up the hill to find the cairns used to stop those beastly Germans from landing planes. With military precision, they were laid out in neat straight lines:


There were hundreds of them! This must have taken ages to construct


Finally I headed a mile south to check out the third control bunker within the farm. I was meant to have asked for permission to enter the farm, but farmers scare me, so I sneaked in like a ninja:


Unlike the other two control bunkers, this one had no earth cover. An anti-aircraft battery was also based here during the war, but I couldn't find any trace of it (my research tells me a barn was recently built right on top of it)

And inside. If I had this in my garden, I would be looking after it and not throwing old tyres in. Just saying.


Thanks for looking. Hoping Ordnance will see this and give us more insight to these starfish sites, as I couldn't find any historical photos.


Read comics and sleep all day, = no worries
28DL Full Member
This is an interesting site!

The Lone Ranger

Safety is paramount!
Staff member
Nice report and an interesting write up, cheers for posting :thumb


28DL Full Member
28DL Full Member
Good job mate, an interesting write-up and some good pics too! Keep up the good work!


28DL Full Member
28DL Full Member
If I had this in my garden, I would be looking after it and not throwing old tyres in. Just saying.
Amazing is it not, that interesting places like this always seemed to be owned by someone who wants to seal it up, fill it in or just abandon it!

Bertie Bollockbrains

There is no pain
Regular User


Irregular Member
Regular User
Fascinating stuff, really enjoyed reading the write up. They had some ingenious ideas to protect the country with little resources back then. Cheers for sharing

Bertrina Bollockbrains

28DL Full Member
28DL Full Member
A very good learning day for me... i never knew things like this was done during the war .
Thanks to Ordnance for the extra info...

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