One of 15 mobilisation centres built in the 1890's as part of a comprehensive military scheme known as the London Defence Positions drawn up to protect the capitial in the event of invasion. The percieved threat came about due to advances in warship design and doubts about the Royal Navy's defencive capability. Essentially a contingency plan, it provided fro the establisment of a 72 mile long, entrenched stop-line of ten sectore supported by artillery batteries and redoubts. The stop-line ran from the southern edge of Surrey and Kent Downs, up the western side of the Darenth Valley to the Thames and then north from Tilbury Fort to Epping. No two centres were alike although broadly similar, adopting the Twydall Profile, depending on whether they were built for infanty or artillery.

By 1905 confidence in the RN had been restored and the centres, now obselete, were abandoned and sold off.

The probable date of the Westerham centres construction was around 1900 at a cost of £9,030. Early plans indicate the intention to construct three stores and five casements here set into the front of the rampart. Later amendments reduced this to two stores, one cartridge store and three casements. The elongated earthern rampart enclosing the magazines and casements was closed at the rear by a concrete wall piecred by two entrances that were closed by bullet proof, looholed steel gates. Set in the wall between the entrances was accommodation for the caretakers. Here the standard layout of the caretakers cottages was not followed probably due to the gorge wall which formed a shallow "V". This accommodation would have been taken over by troops in an emergancy and all the outward facing windows had loopholed steel shutters. Although accommodation was provided for the caretakers within the centre, a pair of standard caretakers cottages at the entrance to the site were also built, possibly to free up more room within the centre.

The centre has subsequently partly built upon, the rampart cut back and the walls, gates and traverse removed, although the magazines and casements still exist as well as the caretakers cottages at the entrance.

Occupiers of the centre recall troops, possibly Home Guard, at the centre during WW2, though why they were here is not known.(1)

<1> Palmerston Forts Society, 2000, The London Mobilisation Centres, Pages 66-68 (Monograph). SKE7544.