This structure was completely below ground with raised entrances level to the surface and was aligned north-east to south-west. The north-east entrance was 52cm above the chamber roof and measured 6.3m long by 1m wide. It was capped by corrugated iron covered in concrete, which sat upon a lip in the entrance wall, which was 5cm deep at the sides and the chamber end of the entrance. This entrance was blocked by earth and rubble so it was not possible to ascertain the number of steps. The entrance led down into a corridor (70cm wide), ending in a recess (87cm deep), with a centrally-located 10cm-diameter exhaust vent. The south-west entrance was 66cm above the chamber roof and measured 6.25m long by 1m wide. This was capped with concrete covered corrugated iron that sat on a lip that was 5cm deep at the sides and 10cm deep at the chamber end of the entrance. The entrance had twelve steps that led down into a corridor that terminated in an 87cm-deep recess with a 10cm diameter exhaust vent centrally located in the roof. Both entrance corridors had a poured concrete floor with five 60cm by 46cm concrete slabs set into them.
The central chamber was identical to shelters F1-F5 in terms of measurements and fittings. <1>