Demolitions used for protective purposes could either be strategical or tactical.
Strategical demolitions have a prolonged effect upon operations over a wide area and involved extensive demolitions throughout a belt or belts of country with a view to delaying the enemy advance and hindering his supply system.
Tactical demolitions aimed at checking the forward movement of the enemy or giving flank protection to defences. Such demolitions could involve minor obstructions such as the destruction of small bridges or blocking roads with craters. Perhaps the most common form of such demolitions was the destruction of all bridges over a watercourse. Tactical demolitions could either be undertaken independently of, or in conjunction with, a strategical demolition plan.
The value of any demolition lay in the delay posed on the enemy. The creation of a temporary obstacle may be sufficient in some cases but the delay will be considerably increased if passage of the obstacle could be hampered by fire (artillery or small arms) or by air attacks.
If demolitions are carried out in an uncoordinated or isolated manor, they would have only a local effect. It was important that any demolition scheme should be carried out to a definite plan to ensure an effective obstacle.
A strategical demolition scheme usually comprised of a primary belt of demolitions to create an effective linear obstacle. The primary belt was then extended laterally and in depth to by subsidiary belts or zones of demolitions.
In respect of carrying out demolitions, demolitions were classified as:
- Preliminary demolitions that could be carried out at once.
- Deferred demolitions that would be executed as late as safety permitted.
- Final demolitions that would be executed by rear guards in contact with the enemy.
In the context of Britain’s anti-invasion defences, demolition policy was complicated by the requirement not to unduly hinder the civil population or to hamper any counter-offensive action. Also the supply of explosives (along with everything else!) was limited and any demolitions actually carried out would have to be were they were most urgently needed.
In Eastern Command the following demolition belts were prepared in 1940:
- Forward of the Command Line – exits from ports and beaches (with subsidiary belts along the water obstacles on Divisional Stop Lines).
- The Command Line
- The G.H.Q Line
In addition, in 11 Corps the River Waveney and Back Line were organized as Demolition Belts.
Demolitions prepared in these belts could equally act as Tactical Demolitions – e.g. for landward defence of ports.
Demolitions were in effect Deferred demolitions and could not be undertaken until “Action Stations” had been ordered and orders received from a named officer authorized to order the firing of the charges. The only exception was if they in effect became Final demolitions i.e. under immediate threat of capture by the enemy. Eastern Command delegated the authority to fire demolitions to Sub-sector Commanders. In forward areas, Sub-sector Commanders could further delegate to Battalion Commanders, who could further delegate to Company Commanders if the demolition formed part of a Company locality. Such delegation was to ensure that the demolition could be fired in any case where the enemy approached the demolition in greater strength than the guard could deal with. In the case of the Back Line, authority was retained by the Division.
Due to the need not to hamper either the civil population or any counter-attack, any demolition carried out should not take more than seven to eight days to restore. The only exception to this was road bridges which gave direct access to ports – these could be prepared for major demolition provided that they could be readily replaced by pontoon bridges or other emergency bridges. All other demolitions of road bridges were only to produce a “reasonable” gap. Railway bridges were not to be prepared for demolition unless they provided an effective crossing for a tank over a designated Stop Line which could not be effectively blocked by a derailed truck.
Authorization was given to charge all prepared demolitions within 20 miles of the coast with the exception of road bridges over five miles from ports (those within five mile of ports could be charged). Railway bridges that provided effective tank crossings over Stop Lines could be prepared for demolition but not charged. Detonators were not to be placed with any charges put in place! Any charge that was put in place had to be guarded unless it could be secured in an adequate chamber. For the Command Line and G.H.Q. Line the charge had to be prepared but not placed; it had to be stored near the site and kept under lock and key. Demolition Parties were to proceed to demolition sites on “Stand To”.
Above: Main Demolition Belts in Suffolk