Inter War Field Defences

This post has some brief notes on  the tactics of the British Army Field Defence form the end of the First War to the end of Second War with reference to various manuals of the time. Some principals of defence remained throughout – namely depth to the defence.  The defence was largely linear from the end of the First War to the start of the Second. Experience at the start of the Second War showed that a commander could no longer maintain a continuous defensive line since the concentration of overwhelming fire power, including air attack, will enable  the attacker to penetrate the defence, even through its full depth.

During the First War, a stale mate on the Western Front developed in 1914, with both sides digging in. Throughout 1915-1916 defences consisted of a linear system of trench lines.  Experience soon showed that if an attacker concentrated his forces and artillery on a particular point, a break through could be made. However a lack of reserves to exploit any breakthrough and also a lack of mobility resulted in the defender being able to consolidate his line.

Although the Battle of the Somme started off badly for the Allies, eventually a series of well planned ‘bite and hold’ battles had pushed the Germans back to their third line in many places by the time the winter weather closed down the battle in Nov 1916. Both sides were worn out and had suffered horrendous casualties. The German Commander in Chief, General von  Falkenhayn was dismissed on Sep 5^th after the failure at Verdun and the high losses suffered on the Somme. He was replaced with Field Marshall Hindenburg and General Ludendorff.

Hindenburg and Ludendorff immediately changed tactics.  General von Falenhayn’s ‘first principal in position warfare’ was to hold ground to the last and to retake any ground lost by immediate counter-attack. Such tactics were one of the reasons for the heavy loses suffered by the Germans. The new tactics were less rigid, based around defences organized in a deep zone rather than a front line trench which could be smashed by artillery. In order to conserve forces and allow for a period of stable defence, a decision was taken soon after Hindenburg and Ludendorff took command to construct such a defence system in the rear.  Work soon began on the first of five planned such systems, the Siegfriedstellung (know as the Hindenburg Line by the British).

These new defences took the form of an outpost zone and main or battle zone. Behind the main zone, Eingiff (alert) divisions would counter-attack any attackers who had penetrated the forward zones.  The attacker would have to first penetrate the outpost zone which would take the first shock of the attack and then advance to the battle zone when he would be out of range of his supporting artillery but within range of the defenders artillery. The battle zone consisted of mutually supporting strong points (each with counter-attack reserves) designed to split up and canalize the enemy attack when the Eingiff divisions could then counter attack and destroy the enemy. This system was more or less copied by the British and was basically the method of tactical defence right up to the start of the Second War.

Hindenburg Line and Hindenburg Support – Moevres, 1917

British Trenches in Fontaine area, Fifth Army 1918. This trench system and the German Hindenburg line comprised a defence of mutually supporting redoubts linked by communication trenches arranged in a deep zone. The defence system is however still linear in nature

British trenches in Travecy area, Fifth Army 1918. Here the Battle Zone is much less complete than the above image

Field Service Regulations, Vol II 1924; Manual of Field Works (All Arms) 1925

These manuals emphasized defence in depth was necessary to resist attack from modern weapons. To obtain this depth, the defence was organized with:

• A forward or covering zone
• A main zone

The object of the garrison of the forward zone was to keep a watch on the enemy, give warning of any attack and absorb the first shock of any attack. It was to be organized with a chain of sentry posts and mutually supporting defended posts organized in depth.

The main zone would be the area in which the battle would be fought. It would be organized in depth and strengthened with obstacles. Machine guns would form the framework of the defence and would ideally be sited in pairs to enfilade tactical localities and cover the approaches of the enemy.  The infantry defence consisted of a series of ‘Defended Posts’ – a series of trenches suitable for a section. These could be hastily constructed posts in mobile warfare or groups of posts joined by trenches in a complete defensive system. In this case they would be grouped into ‘Defended Localities’ – an area defended by a definite unit such as a platoon or company, comprising  of groups of Defended Posts so sited to cover all the ground to the front and flanks as well as neighboring localities and connected by communication trenches.

Defended Posts – Manual of Field Works (All Arms) 1925

Defended Locality for a Company – Manual of Field Works (All Arms) 1925

An important aspect of the defence was obstacles. These were to be used to check or direct the movement of the enemy troops and hold them under fire as long as possible. Obstacles were of two types:

• Tactical – intended to break up an enemy formation, restrict his power of manoeuvre or force his troops into a position in which they could be dealt with by the weapons of the defence.
• Protective – intended to hold the attackers under close rifle fire of the defenders.

Defensive system showing use of Tactical and Protective obstacles – Manual of Field Works (All Arms) 1925

Full consideration was also to be given to anti-tank obstacles. Examples of anti-tank obstacles included mines, a ditch 10ft wide and 6 ft deep, concrete blocks about 2 ft cubed at 5 ft intervals and tank traps (pits 10 ft wide and 6ft deep covered with light material to hide them).

Anti-tank obstacles – Manual of Field Works (All Arms) 1925

Field Service Regulations Vol II 1935

Military Training Pamphlet No. 23 – Operations Part II: The Defence, 1939

Again defence in depth is emphasized as essential against modern weapons. As above the defence was to consist of a forward belt of defended localities arranged in depth and mutually supporting. The defence was then built up in depth in rear of the forward belt. The plan of defence was to be based on fire power rather than men – the co-ordinated fire of all weapons (artillery, machine guns, light machine guns, rifles and anti-tank guns).

Counter attack was also a key part of the defence although the decision to counter attack with local reserves or use the force defensively to localize any enemy success was a difficult decision. All ground lost was not to be re-taken by counter-attack as a matter of routine. The decision would depend upon whether the ground lost was key to the defence or a reasonable chance of success against enemy forces.

The development of the defence would consist of initial sighting of weapons-pits. If the position was to be held for any length of time the pits would be developed into fire trenches linked with communication trenches. Defended localities would also be linked by trenches to prevent individual localities being recognized as isolated earthworks. If the defence was to be protracted, defences would be strengthened with deep dug-outs, wide belts of obstacles and concrete emplacements.

Weapons-pits linked by Communication trenches to form a platoon post – Manual of Field Engineering (R.E) 1936

Concrete machine gun post – Manual of Field Engineering (R.E) 1936. Pillboxes clearly based on this design can be found on parts of the GHQ line and in Norfolk

The 1939 pamphlet set out the latest ideas on defence, although still based on Field Service Regulations 1935. The main development in thinking was highlighting the anti-tank defence. The main zone of defence should be protected by a continuous anti-tank obstacle. The rear area, where reserves were located, should also be protected by an anti-tank obstacle and was to be were any enemy attack, if it had penetrated as far, could be bought to a halt. There was also a growing recognition of the value of air power in the defence.

Anti-tank obstacles – Manual of Field Engineering (R.E) 1936

Military Training Pamphlet No. 23 – Operations part II: The Infantry Division in Defence, 1942

Military Training Pamphlet No.3 – The Defence, 1943

The 1942 pamphlet noted how a modern attacker, with armoured fighting vehicles, working in co-operation with aircraft and airborne troops had opened up the battlefield. The defender must now expect to be attacked from the rear by airborne forces and for enemy armoured columns to make deep penetrations into the defence in places. Mobile armoured and motorized reserves were vital

Although the defence was still based on localities in depth, the emphasis was now much more on anti-tank defence. The defence was now to consist of a system of anti-tank localities. It was emphasized that the modern battle was largely fought along the road systems. Defended anti-tank localities should be sited to deny the use of the roads to the enemy. The entire position was to be covered with a tank obstacle if possible – either natural (e.g. river) or by linking up localities with anti-tank ditches or minefields.

The 1943 pamphlet highlights the fact defence could no longer be static but had become offensive by the use of powerful highly mobile counter-attack force to destroy any enemy penetration. Obstacles should not be relied upon to halt or delay the enemy but rather to disrupt the attack and canalize the attack into areas where they could be dealt with by the weapons of the defence.

Defended area held by a Corps. Defence no longer linear but based on localities protected by obstacles to disrupt and canalize an enemy attack with mobile counter attack forces in reserve

In conclusion the defence, always in depth, changed from a largely static linear system to a much more aggressive defence based around powerful counter attack forces. This can be seen in the tactics employed in Britain’s anti-invasion defences. Ironside, with little option at the time, planned a defence in depth based on defended localities protected by anti-tank obstacles. It was largely linear with the beach defences (or ‘Coastal Crust’) forming the first line of defence and a series of anti-tank Stop Lines  inland.

These Stop Lines were designed to delay or halt the enemy attack and allow the deployment of the mobile reserve in counter attack. The GHQ anti-tank Stop Line was to be the final line where any enemy attack was to be finally halted if it penetrated that far. General Brooke envisaged a much more aggressive defence.  By 1941 Home Forces were ordered to abandon the concept of ever manning the GHQ line. Instead inland defences were to be based on a network of anti-tank islands and centers of resistance.

Many key towns and villages on the GHQ line were readily adapted to anti-tank islands. Elsewhere other key nodal points had their defences developed. These islands were to hold out long enough to allow mobile counter attack forces to reach them and destroy the enemy forces that had penetrated that far.

References:

Ironsides Line, C Alexander, Historic Military Press  1998

German Assault Troops of the First World War, S Bull, Spellmount, 2007

The Hindenburg Line, P Oldham, Leo Cooper, 1997

Manual of Field Works (All Arms), W.O, 1925

Field service Regulations Vol II, HMSO, 1935

Manual of Field Engineering (R.E.) Vol II, HMSO, 1936

Military Training Pamphlet No. 23 – Operations Part II: The Defence, W.O, 1939

Military Training Pamphlet No. 23 – Operations part II: The Infantry Division in Defence, W.O,1942

Military Training Pamphlet No.3 – The Defence, W.O,  1943