CAB80-20 — Page 76

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(c) The arrival of the main force at a major port, or

ports, capable of handling a large number of ships simultaneously.

(a) Subsidiary landings on a small scale at other ports.

SEABORNE ATTACK.

The availability of shipping.

5.

The Germans are known to have 300,000 tons of suitable shipping in French Ports south of (inclusive) Brest, and they have proved themselves capable of moving shipping westwards along the north coast of France.

The possibilities of interception.

6.

Though the concentration of troops at suitable perts might indicate the intention to invade Eire, it would not ̈

Such give warning that invasion was necessarily imminent.. warning might be obtained from: indications of troops being loaded, but will largely be dependent on visual reconnaissance.

7.

It can clearly be only a matter of time before the sea communications of the invading forces would be seriously interrupted by British naval action, though it cannot be categorically stated that they would be definitely cut. Thus once the presence of the invaders was known, they could not count upon running more than isolated ships past our naval patrols. Their plan would therefore have to aim at getting the whole of their essential requirements in one flight into protected anchorages in ire before they could be intercepted. The resultant concentration of shipping would be extremely vulnerable to air and naval attack, but this is a risk which they might be prepared to accept as they could provide a measure of fighter cover, and since no other course would be open to them. We discuss, in greater detail the question of vulnerability to air attack in paragraphs 17 and 18 below.

8.

Though an immense armada would be required to transport the whole expedition in one flight, we cannot ensure its detection in conditions of poor visibility, which may well last over a period of days. At 10 knots the passages from the Gironde and Lorient to Cork are 48 and 38 hours respectively. From Norwegian or Baltic ports the passage would be much longer, and the prospect of interception greater, as the expedition would have to pass through areas of intense naval activity traversed by two main convoy routes, and largely covered by air patrols.

9.

It must be realised also that the maintenance of such forces as could be landed would not involve a large shipping commitment. On the scales that the Germans might be expected to adopt for a short campaign, mainvenance might involve

It is not possible only one ship per division per week.

to guarantee that occasional ships would not slip past our patrol,

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