Monument record SBT 036 - Sibton, Auxiliary unit operational base

Sibton Auxiliary unit operational base (S1).
The operational base was built into the steep bank of a small stream skirting the edge of mature woodland (Kendall’s Wood) near South Green / Grove Farms. The main chamber and entrance shaft are intact but the emergency exit tunnel had collapsed and was excavated in 2001/2. The OB consists of a 12ft Nissen hut resting on a base of red brick, with end walls and the drop down entrance shaft built from red brick. The entrance shaft cover is missing, and access is provided by a series of steel rungs set across one corner (S2).

The main chamber and entrance shaft are intact but the emergency exit tunnel has collapsed and was later excavated. The main chamber measures: (L) 3.65 x (W) 2.45 x 2.40m (at highest point) and is orientated NNE/SSW. The drop down entrance shaft measures 0.75 x 1,00 x 3.00m deep (approx). Length of emergency exit tunnel is 6.00m. Other physical remains are corrugated iron sheets originally used for lining the walls of the emergency exit tunnel. These were removed during excavation and dumped beside the entrance opening. 3 concrete counterweights, pitched, with pivots made from gas piping: 0.45 x 0.40 x 0.15m (approx). There is also a field drainage pipe across one corner of entrance shaft presumably carried phone cable or coax aerial cable. The OB consists of a 12ft Nissen hut resting on a base of red brick, with both end walls as well as the drop down entrance shaft built from red brick. The entrance shaft cover is missing. Steel rungs (badly corroded), set across one corner, provided access. The entrance shaft and main chamber are intact and in good condition, the curved corrugated iron roof of the main chamber is corroding from the base upwards. A (broken) field pipe is set across one corner of the shaft approximately one metre below ground level. The pipe is set into the wall above the entrance doorway. It runs in the direction of a nearby tree and in all likelihood carried either a phone or a coaxial aerial cable. There is an approximately 15cm long nail almost completely embedded in the tree directly in line with the field pipe at about 1.80m above ground level. The main chamber houses the original three concrete counterweights . Two recesses - one on each side of the entrance from the drop-down shaft into the main chamber – accommodate vent pipes which emerge above ground level on either side of the shaft entrance opening. The doorways of both entrance and exit are facing each other. Stephen Lewins/CART points out that “The doorways have an unusual curve to the top, normally they didn’t go to so much trouble.” Unusual also the two recesses accommodating the vent pipes. The emergency exit tunnel measures about 6 metres in length, leading away from the main chamber in a straight line and emerging about one metre above the bed of a small stream which at the time of our visit (early July) carried no water. The tunnel had collapsed and was dug out and made safe (walls stabilised at some time during the past 10 years.) (S3)