The fear of an invading army landing on either the south or east coast, and marching on London resulted in various schemes being suggested to defend the capital with fortifications. The scheme finally adopted originated from a memorandum drawn in 1888 up by Colonel Ardagh, A.A.G. He envisaged the construction of about 30 small works, capable of expansion to form a series of “points d’appui” for entrenched positions which would bar important roads and also act as storehouses for entrenching tools and ammunition.
A committee was established to draw up a scheme for a defensive line around London, based on a line north of London (from Vange by Brentwood to North Weald) and south of the Thames (along the chalk ridge from Guildford, by the Darent Valley to Dartford). The positions were known as the London Defence Positions. Authority to start acquiring sites and constructing small works and storehouses, or so called “Forts” was given in 1889 and 1890. Most were constructed south of London, along the crest of the North Downs. The only “Fort”, or Mobilization Centre as they were referred to, constructed in East Anglia was the North Weald redoubt. These redoubts were designed along the principle of the Twydall Profile, after an experimental redoubt constructed at Twydall. The redoubts consisted of a gentle parapet sloping from a shallow ditch in which was placed a steel fence. Shelters for the garrison and stores were built under the parapet.
By 1900 changes in tactical ideas resulted in a need for a revision of the London Defence Positions. A temporary scheme was drawn up and this scheme formed the basis of the Handbook of the London Defence Positions produced in 1903. The general principles of Home Defence in the Handbook were stated as:
No enemy would attempt an invasion unless he had control of the intervening seas
The principle target of any invasion force would be London.
A recognition that small scale raids on major ports and arsenals were a possibility.
The general principles of the scheme for Home Defence were that:
A Field Army would be available for Home Defence although its strength would depend on whether an Expeditionary Force had been deployed or not. The role of the Field Army was to defeat the enemy in the open field after he had landed and his main advance had declared itself.
A Volunteer Force (10 Divisions) would be available for deployment to the selected positions around London and would include a force of heavy artillery.
The Coast defences would consist of Garrisons of Fortresses and Mercantile Defended Ports and mobile columns to defeat minor raids.
That unless the Navy was crippled and unable to interfere with the transportation of the invasion force the enemy would be keen to reach London by the shortest roads which would make the most likely landing place somewhere between Portsmouth and Harwich. The coast between Great Yarmouth and Harwich was the second most likely stretch for an invasion force to land. It then followed that the best area for concentration of British defending forces was to the north and south of London.
Hence the Field Army would, on concentration, be distributed along a front extending from Aldershot by Gravesend to Colchester. Behind this front the Volunteer Force was to be posted to selected defence positions north and south of London.
The first duty of the Volunteer Force would be to complete the selected defensive positions. Depending upon the situation, the Volunteer Force could move up to support the Field Army, or the Field Army may fall back to the defence positions.
The London Defence Positions, south of London, extended south of the Thames, from a point five miles west of Guildford, on the Hogs Back, eastwards along the main chalk ridge, by Dorking and Reigate, to the valley of the Darenth, near Halstead, whence it followed the western slopes of that valley as far as the Thames at Dartford. The total length of the line south of the Thames was 48 miles.
North of the Thames, it extended northwest through Essex, from Vange on the Hole Haven Creek, by Laindon, Brentwood and Kelvedon Hatch to North Weald (Epping). The length of the line north of the Thames was 24 miles.
Although the intention was to entrance the whole line, it was dived into 10 key Positions, six south of the Thames (Guildford, Dorking, Redhill, Godstone, Westerham and Darenth) and four north of the Thames (Laindon, Brentwood, Kelvedon Hill and North Weald). The Guildford and Darenth Positions had entrancements thrown out on their left flanks, known as the Shere and Darenth Valley Extensions.
In addition, there was an outpost position at Wrotham, liking the London Defence Positions to the Chatham Fortress. It controlled the main road from Maidstone to London and so hindered any enemy flank movement on Farningham or Dartford.
By the time the Handbook was produced, a number of permanent redoubts / Mobilization Centres had been constructed to keep tools and ammunition in peace time and to be used as tactical pivots during war time. This included the North Weald redoubt in East Anglia.
The decision to start work on the London Defence Positions was taken in 1915 as fears of invasion increased. The entrancements carried out largely followed the plans laid out in the Handbook. Eventually three defence lines were completed, the main London Defence Positions, an outer position at Brentwood and a third line running from Chelmsford to Maldon.
Above: Constructing the London Defence Positions