The Danger Area Shifts to the Western Approaches
It was expected that the German Naval Command would take advantage of the great strategical possibilities offered by the occupation of Trondheim and Lorient to attempt to strangle the import trade of the British Isles by submarine attack and by naval raiding forces. On the 17th August 1940 the German Command proclaimed a “total blockade of the British Isles”; and, during September, simultaneous with the attempt by the German air force to gain air supremacy, the submarine campaign was intensified particularly in the waters off the west of Scotland and in the North-Western Approaches.
Our ability to carry on the war depended upon the maintenance of supplies through the West coast ports by the north-about route around Ireland. In September imports dropped to about 800,000 tons or 23 per cent. less than for May 1940 (over 1,000,000 tons). The minimum requirement had been put at 60 per cent. of the May figure, so that although the falling off was considerable the decline was as yet far from being a total blockade. In addition to that threat, the march of events in South-East Europe compelled us to accept the risk of sending reinforcements to the Middle East to the limit of our shipping capacity.
Diversion of Naval Forces from Anti-Invasion Duties to Trade Protection
At the end of October the First Lord of the Admiralty, Mr. A.V. Alexander, pointed out to the Defence Committee that our shipping losses in the North-Western Approaches were most serious, the tonnage lost being in excess of replacement by purchase and new construction. He added that if the existing rate of losses were to persist our reinforcement programme overseas would have to be curtailed, and it might prove impossible to maintain large forces in the Middle East.
The C.-in-C. Home Fleet, Admiral Sir C. Forbes, agreed that unless our anti-submarine craft on the North-Western Approaches were substantially increased there would be a grave danger of losing the war by the interruption of our life-line with the United States and the Empire.
That threat to our overseas trade routes caused the diversion to trade protection of more than half of the naval light forces allotted to anti-invasion duties; and the Prime Minister asked the President of the United States to sanction the purchase of fifty American destroyers as a reinforcement.
By the Spring (March 1941) the Battle of the Atlantic had spread to the whole of that ocean. In addition to their ocean-going submarines the Germans had a number of efficient surface warships and raiders in Northern Waters, and it had become necessary to convoy right across the Atlantic. Shipping was being attacked too, off the West coast of Africa. In the circumstances, heavier ships of the Home Fleet had to be dispersed to distant ports, ready to join as escort if necessary.
Reduced Anti-Invasion Naval Forces Based on Plymouth and Rosyth
The vital need to guard adequately our Atlantic trade routes was not the only cause of the reduction in immediate naval assistance to counter an attempted invasion. Owing to the threat of dive-bombing attack and to the continuous sowing of mines by German aircraft the naval authorities proposed to base the naval anti-invasion forces on ports down the Channel, such as Plymouth, rather than on the restricted East coast; and the East coast cruiser squadron on Rosyth.
The Defence Committee accordingly noted on the 31st October that the Army would have to be prepared to hold the beaches in South-East England, with such assistance as the Air Force could afford, until the arrival of naval forces strong enough to intercept the enemy’s sea passage. That “period before relief” of the troops guarding the beaches was estimated at 12 hours, i.e. the time of passage at 20 knots from Plymouth to Dover.
Erection of Beach Scaffolding as a Delaying Measure
As some compensation the Admiralty was asked to consider the erection along the most vital beaches, particularly in the North Foreland–Dungeness area, of fixed tubular steel scaffolding to check the first waves of an invasion attack. Experiments had shown such an obstacle to be unclimbable and proof against tanks. Compared with the proposed under-water nets, too, the scaffolding would last for three years instead of three months, and it could be made of lower grade steel. The scaffolding was to be erected above high-water mark as an antitank obstacle; if placed in shallow water it was proof against light craft but could be penetrated by heavy barges.
The Admiralty to have Operational Control of RAF Coastal Command
In order to be able to deploy the maximum possible force in the air for action in the North-Western Approaches, and to enable a single authority to be responsible for bringing in the convoys, the Admiralty asked that the Air Ministry should hand over “the whole of Coastal Command, R.A.F. complete”. In the opinion of the First Lord, Mr. A.V. Alexander, they could not assume full responsibility for the protection of convoys unless they had control of the operations equipment and training of the air squadrons of Coastal Command. He believed that the transfer could be effected without difficulty.
The Prime Minister thought that if they had been starting afresh in peace-time the great change proposed might be desirable; but “it would be disastrous at the present moment to tear a large fragment from the Royal Air Force”. The Committee agreed that Coastal Command should remain an integral part of the Royal Air Force for administration and training, but that for all operational purposes it should come under the control of the Admiralty. In the event of a difference of view between the Admiralty and the Air Ministry the number and type of aircraft to be allotted to Coastal Command should be fixed by the Defence Committee (Operations).
The Admiralty took over operational control of Coastal Command R.A.F. on the 15th April 1941.
The Problem of Eire
An attack upon Eire from French ports might be made either as a diversion in the event of an invasion of Great Britain or as a deliberate move to establish air and submarine bases from which to attack our vital shipping routes.
Whoever landed first in Eire would probably be attacked by the Irish; and to seize harbours and air-bases there against the will of the Government and people would involve a very gave military commitment, though it might have to be done if the threat on our Western Approaches became mortal.
The Defence Committee considered that the maintenance of a successful German landing in Eire was most improbable so long as our naval and air forces were undefeated. Should a large scale raid be attempted, and allowing for losses due to our naval and air action, up to 2 or 3 divisions might be landed from merchant ships with a proportion of tanks, and supported by a maximum of 8,000 airborne troops.
To resist such a landing the armed forces of Eire itself amounted to four brigade groups, arranged in mobile columns of about one company each, with armoured cars; and the Local Security Force, corresponding to our Home Guard, was about 90,000 strong.
Our resources in Northern Ireland were 3 Infantry divisions, one independent brigade group and 2 infantry brigades. The Ulster Volunteers or Home Guard amounted to about 38,000 by the end of May 1941; and in addition 3 Garrison, 4 Home Defence and 2 Young Soldiers battalions were available for guarding aerodromes and other Vulnerable Points.