War Planning: 1918-38


Britain ended the First World War with perhaps the best equipped and trained Armed Forces in the world. However this state of affairs was not to last long. Post war strategy was to try and prevent wars in the first place by mediation and a system of collective security through the newly established League of Nations. Another war in Europe seemed so unlikely in the next 10 years and this assumption was re-affirmed in 1928 (the so called ’ten year rule’). The affect of this in terms of planned defence spending was to see spending slashed on the Armed Forces. The rise of Hitler and National Socialism in Germany in 1932 gave cause for concern and the Government cancelled the ten year rule and arrangements were put in place to remedy the deficiencies in the Armed Forces and to plan for war. However almost up to the outbreak of war, the Government and Chiefs of Staff had different views on planning for war.


Prior to the German occupation of the Rhineland in 1936, the defence of Great Britain was based on maintaining a powerful air force as a deterrent.  Neville Chamberlain expressed this view in 1934 – “it stands to sense that our policy should be to construct the most terrifying deterrent to war we can think of, and recent advances in the design of aircraft and engines give us the weapon best calculated to affect that purpose”. The Chiefs of Staff best envisaged using this deterrent from a forward zone on the Continent in order to be as close as possible to vital German targets and also keep the German airbases as far away from Britain as possible.  In order to secure a safe forward zone on the Continent the cooperation of a modern and fully equipped Expeditionary Force would be needed.  It was recognized that Britain was still vulnerable to air attack from Germany, especially with a quarter of the population concentrated in the South-Eastern corner of England. The “distant defence” of Britain was to be backed up with a “close defence” based on fighter aircraft and anti-aircraft guns.


The “close defence” scheme was based on a continuous defence zone, 26 miles deep,  around the South-East and East coasts from Portsmouth to London then north to the Tees. This zone was divided into an outer artillery zone, six miles deep, comprising of anti-aircraft guns and search lights designed to break up German bomber formations.  Behind this was the aircraft Fighting zone, 20 miles deep, where fighters would attack the broken up bomber formations. Behind the forward zone was the inner artillery zone (or gun defended areas) protecting London and major industrial centers.









































                                           Above: 1935 plan for the Air Defence of Britain



The Government rejected the Chiefs of staff plan of a “distant defence”, largely on the grounds of cost and instead relied on building up a strong air force and sufficient air defence system as a deterrent to war. This was at the expense of the army and navy.


 The German occupation of the Rhineland, carried out in defiance of the Lorraine Treaty and the League of Nations, was in effect a declaration of war and also showed their disregard of Britain’s air force as a deterrent. Italy and Japan, seeing the change in the balance of power made common cause with Germany and Belgium declared her neutrality.


This change in circumstances led to the Chiefs of Staff memorandum on “Planning for war with Germany” - February 1937. They expected that Germany would try a knock out blow from the air on either France or Britain, with Britain being the more likely target. A German invasion by land or air was considered very unlikely given Britain’s air and naval power – on 7th Feb 1937 the Committee of Imperial Defence maintained “so long as our Navy and Air Force are in being, a sea-borne invasion could be defeated without the help of land forces…….and the danger of an airborne attack on a large scale is negligible”. The Chiefs of Staff again pressed for a fully equipped and modern Expeditionary Force to give immediate assistance to the French to stop any attempted German expansion westwards.  The “close defence” scheme was also amended by extending the Fighting  Zone to include the Tyne, Forth and Clyde (as a result of the increasing range of German bombers), the minimum number of fighter squadrons increased to 38, the number of searchlights doubled to 4,684 and anti-aircraft gun equipment trebled to 1,296.


The recent development of radio direction finding (R.D.F) resulted in the planning for a chain of 22 R.D.F stations by 1939. It was envisaged this would give fighters enough warning to climb and be ready to meet the bombers at or near the coast. As a result anti-aircraft guns were to be withdrawn from the coastal artillery zone and used to reinforce the inland gun defended areas.


This was a minimum requirement and in reality Britain in 1938 was nowhere close to this level. Only 27 Fighter squadrons were available as at March 1938, many of the anti-aircraft guns were of the old pattern 3 inch which did not have an adequate range and of an approved order for 640 3.7 inch and 4.5 inch guns only seven had been delivered.


The Government’s view on this was that as the priority was the defence of Britain, the first priority should go into maintain a strong fighter force (at the expense of an air striking force). Second priority was the protection of trade routes so the Navy was to build up a fleet to be based in Home Waters adequate for a war with Germany.  The third priority was the maintenance of the regular army at home to be able to act as an overseas Imperial Police force. As it was considered that any such actions would not be prolonged, a reduction of reserves and heavy tanks was considered as possible. The fourth priority was the assistance of the defence of the territory of any allies. If France was overrun “an army would have to be improvised”. The defence against any sea-borne or air-borne invasion of Britain came last in the Army’s task given the risk was still considered as negligible.  


The Munich Agreement in Sept 1938 led to the loss of 30 Czech divisions and as a result the French asked for assistance on land. The Chiefs of staff considered that France may not bare the brunt of fighting on land on her own and the loss of the Channel ports was considered such a grave threat that the provision of an Expeditionary Force should be of the highest priority.  The Government this time agreed. In April 1939 after the annexation of the Czech state, the Cabinet agreed to bring 13 Territorial Divisions up to strength and when this had been done, to double the force. Conscription was introduced on April 17th to achieve this and the Ministry of Supply was created to provide for the expansion.


On Sept 2nd, following the invasion of Poland, France and Britain declared War on Germany. The threat of invasion of Britain was still not considered a risk and the Government planned on a long period of defence while a gradual build of the army would take place to eventually allow for a counter-offensive into Germany.  The worst case event that Britain would have to face was still considered to be an attempt at a knock-out blow by the German air striking force.




Defence Plans for the United Kingdom, TNA