During July the scale of the likely force to be employed by Germany in an invasion was reassessed. It was considered a force of five divisions (75,000 troops) supported by 15,000 airborne troops could be landed on the first day. Embarkation ports were considered likely to be between the Dutch coast and Cherbourg – to give the shortest crossing. The most likely landing places were between The wash and Newhaven – to allow for maximum fighter coverage. Germany was thought to have up to 100 divisions available to support the initial landing. It was expected the German Navy would support the invasion with its lighter vessels – destroyers, motor torpedo boats and submarines but would be unlikely to risk her battle cruisers in the southern part of the North Sea.
Any invasion attempt would have three stages:
1. The concentration of shipping at embarkation ports
2. The crossing
3. The landings and establishment of a bridgehead.
The Air Force and the Navy were expected to be the decisive elements in defeating any invasion (their role to be looked at in following pages) by destroying the invasion fleet before it reached these shores.
The main principal for the land forces was to be maintained at a level which would require Germany to employ a large force for any invasion attempt which would provide a big enough target for the Royal Navy and Bomber Command and also to make any enemy preparations obvious by aerial reconnaissance. It was assumed that the Navy would have a good chance of intercepting any invasion force and also that any force that succeeded in landing could not be maintained (especially if outside the Narrow Seas). The role of the Army was therefore to destroy the first wave of any invasion force that succeeded in landing.
Some arrangements had been put in place for the co-ordination of the various Commands in the event of invasion. C.I.C Home Forces was to take command of all inshore and land forces while the RAF Commands would try and carry out his washes as far as possible. C.I.C Home Forces had a liaison Naval and Air Staff officer at his Battle HQ. Area Combined HQ’s with staff from the Army, Navy, and Coastal Command were located at Rosyth, Nore, Plymouth and Liverpool. However Brook still thought that this was insufficient for a Combined Command – he felt that “there were far too many commanders” and that there was “no co-ordinating head to this mass of commanders”.
The coast between the Wash and Dover was still considered to be the most vulnerable to any landing. Between Dover and Cornwall, it was not considered to be such a high risk as it was expected the Navy and Air Force would prevent the movement of a large amount of shipping through the Dover Straights to potential French embarkation ports. The West coast was considered to be the least at risk.
The coast, as in Ironside’s plan, was to be held as an outpost zone. Beach divisions could still expect little in the way of immediate reserves. The mobile reserves were mainly held in the Wash- Newhaven sector, were they would be provided with maximum fighter cover and be near the expected main enemy objective, London.
The First Sea Lord had one major reservation about the plan. German long range guns at Cap Gris Nez could already deny part of the Dover Straights to the Royal Navy. If the Germans could land a force by surprise, especially for example in conditions of fog and capture Dover, the whole of the Dover defile would be denied to the Navy, allowing the Germans to land as many tanks and equipment as required. The only defence would be bombing, which was not sufficient alone to stop any crossing, especially at night. The First Sea Lord stated “while coast defences are a “crust” and the main body of resistance would be further back, that rule must not apply to the Dover area where the coast-line must be held at all costs. Under no conditions could we accept that the Germans get any footing there at all”. Brooke agreed stating that another two divisions would be needed in South-east England to make the position secure (the planning for 1941 stated that the Kent and Sussex coast as well as the most vulnerable areas in East Anglia were to be held as the main line of resistance).
Above: Home Forces, Sept 1940 at the height of the invasion scare. The 53rd
and 61st Divisions and the 148th Independent Brigade were stationed in
Northern Ireland, not shown on the above map
On Aug 13th, Goering launched Adlerangriff (‘eagle-attack’) designed to gain air superiority by targeting the RAF stations and control systems. The impact on Fighter Command caused grave concern – by Sept 3rd the available pilots had decreased from 1438 to 840. It was considered that at this rate of attrition, Germany would gain air superiority over the Channel in two to three weeks.
Reports at the beginning of September were received showing hundreds of barges moving towards the Scheldt and Straits of Dover (despite strengthening the Dover coast guns none, including a 14 inch gun, could reach the French coast to attack German shipping). A build up of German short range dive-bombers in the Pas de Calais area were presumably to be used to support an invasion. Moon and tide conditions were also ideal for an invasion between Sept 8th to 10th. These reports suggested that German preparations were so far advanced that invasion could be attempted at any time. On Sept 6th the preliminary Invasion Alert “Attack probable within the next three days” was issued and on the night of Sept 7th Brooke sent out the code word “Cromwell” (Invasion imminent and probable within twelve hours) to Eastern and Southern Commands. The order was repeated to the other Commands for information. However the code word was clearly not understood in some areas and was interpreted to meaning the invasion had started. In places church bells were rang, the Home Guard called out and some bridges actually demolished. The confusion was partly due to the fact that there was no system in place to bring troops to a state of readiness for immediate action in intermediate stages*.
At the crucial moment Hitler switched the German air offensive to London. The invasion never came and with the onset of winter was considered unlikely until the Spring of 1941. GHQ made its assessment of the Home Defence situation, winter 1940 and its plans for 1941.
* The code words “Stand To” and “Action Stations” were introduced as a result to bring troops to a state of readiness in stages above the normal state of readiness to move in eight hours and dawn and dusk “stand to”.
Defence Plans of the United Kingdom, TNA
The Turn of the Tide, A Bryant, Collins, 1957