This structure was completely below ground with raised entrances that would have been level with the surface at the time of construction. Subsequent development raised ground-level, totally obscuring any trace of the structure. As a result of this, shelter F6 was damaged by contractors during their sub-surface excavations and it was not possible to obtain complete measurements for the northern entrance. Once shelter F6 was located and fully exposed, it was observed that the shelter was roughly aligned north to south. The northern entrance was 50cm above the roof of the chamber and was destroyed completely up to a point just outside of the chamber, where a surviving piece was 2.6m long and 1m wide. No steps survived at this entrance and only fragments of the concrete cap remained. The corridor (70cm wide) at the base of the steps did survive and terminated in a recess that was 87cm deep and contained a centrally-located exhaust vent (10cm in diameter). The southern entrance was 55cm above the roof of the chamber and measured 6.45m long by 1m wide, descending eleven steps into a corridor. This was capped by concrete-covered corrugated iron that sat on a lip in the entrance walls that was 5cm deep on each side. The corridor was 70cm wide and terminated in a recess that was 87cm deep and contained a centrally-located exhaust vent (10cm in diameter). The floors in both corridors were of poured concrete with five 60cm by 46cm slabs set into them. A white painted number (51) was observed on a facing panel of each entrance.
The central chamber was externally identical to shelters F1-F5 and appeared to be identical internally; however, due to asbestos contamination, CAT archaeologists were unable to enter the structure. Observational data obtained from contractors confirmed the presence of two benches, square slabs on the floor and an oval shape to the cross-section. <1>