Bofors gun emplacement and attached pillbox

40mm Bofors light anti-aircraft gun emplacement with predictor pit and a detachment shelter,based on a design by the Directorate of Fortifications and Works,built November–December 1940,to defend the Royal Ordnance Factory Chorley,(Vulnerable Point 426).MATERIALS:fair-faced brick walls with concrete gun platform,floors and roof.PLAN:circular-plan,semi-sunken gun emplacement with an attached semi-sunken detachment shelter in the form of a rectangular-plan Type 23 pillbox.EXTERIOR:the circular-plan pit of the emplacement is approximately 4.57m in diameter.The concrete gun floor is approximately 0.6m below ground-level and has a recessed gutter running around its circumference.The emplacement has a low brick retaining wall surrounding it,with four ready-use ammunition lockers set back into the low wall.Situated at the centre of the gun floor is a 1.52m diameter,0.76m high concrete holdfast pedestal.A square cable duct enters the pedestal on the south-western side and rises vertically within the centre of it.A square steel mounting frame with six projecting holdfast bolts is set in the upper surface of the pedestal.A circular brick-lined predictor pit with a cable duct in its floor is situated on the south-western side of the emplacement,and a semi-sunken rectangular-plan Type 23 pillbox is attached to the north-eastern side.The emplacement and the pillbox appear to have been built contemporaneously as one structure.The pillbox is built to a‘blast and splinter-proof’specification,with 0.58m thick walls and the covered chamber has a flat 0.3m thick reinforced concrete roof,and three of the walls are pierced by narrow splay rifle embrasures.The open forecourt to the rear functioned as a weapons pit for a pintle-mounted Lewis anti-aircraft light machine gun(AALMG)and was entered by a gap in the wall at its western corner.At some point in time,the walls of the weapons pit have been reduced in height and are flush with the surrounding ground-level.INTERIOR:the pillbox comprises of a single square-plan room with fair-faced brick walls and a concrete floor,with a central brick-built anti-ricochet wall.It is entered down steps from the weapons pit through a low doorway in the western corner of the pillbox.