What were Britain's defensive plans for a Nazi invasion?

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The Wikipedia article is quite extensive, but the salient points are these:

  • The British army and militia were under-strength in 1940 but with exceptionally short supplies lines and tank production matching then eventually exceeding German production.
  • The British were perfectly willing to gas any invaders and had stockpiles prepared in advance (the British atomic bomb so to speak).
  • The south of England was converted into a battlefield with pillboxes and dragon's teeth to slow German forces and rake up causalities.
  • The Home Fleet, which was beefed up by recalling overseas assets and severely outnumbered the Kriegsmarine. Indeed the 1974 war game to extrapolate the outcome of a 1940 invasion of Britain resulted in a resounding loss to Germany due to the Home Fleet.
  • The population was educated in advance as to their role, to avoid a repeat of civilian paralysis that occurred in continental Europe when the Nazis did the unspeakable.
  • The British intelligence apparatus deceived the German high command as to Britain's capacity to repel invaders so as to encourage the German to misallocate resources or refrain entirely.

As T.E.D. mentions, the British high command would have fallen back to their Commonwealth allies such as Canada had the invasion been successful. In counter-factual history, the involvement of the USA and USSR would have been as vital as in real history.

If the invasion had gone ahead, the unused poster "Keep calm and carry on" would likely been have superseded by the planned slogan "You can always take one with you"

Upvote:1

Churchill always maintained publicly that, worst case, their government would retreat to its colonies (most likely Canada) and try to fight on from there. For example, there is this often overlooked coda to his Fight them on the beaches speech:

... and if, which I do not for a moment believe, this island or a large part of it were subjugated and starving, then our Empire beyond the seas, armed and guarded by the British Fleet, would carry on the struggle, until, in God's good time, the New World, with all its power and might, steps forth to the rescue and the liberation of the old.

However, he was likely telling the USA that at least partly for propaganda purposes. Many in the USA figured the UK would quit the war (eg: Ambassador Joseph Kennedy), and were against giving them any material support that was liable to go to waste with a soon-to-be non-combatant (or worse yet, end up in Nazi hands).

Upvote:1

Basically, the issue was that if the German fleet could get the "first wave" across the Channel, would the Germans be able to reinforce/resupply adequately to defeat the British.

As William L. Shirer pointed out in "The Rise and Fall of the Third Reich," the German navy expected to lose every ship, in a cross-channel landing. That's both war- and transport- ships.

In that case, the Germans would have to be reinforced/resupplied by air, as at Crete. That would have been a tough, almost undoable job. So the main British defense plan would be aimed at preventing reinforcements/resupply, both across the English Channel initially, and subsequently in the air, through anti-aircraft fire. Also, British ships could bombard German land forces from the sea side, catching them in a cross-fire with land-based artillery.

It is interesting to note that (because of the rough weather in the English Channel), the Normandy invasion was given only a 50-50 chance of succeeding (and nearly called off). That's despite the fact that the Allies had complete air and naval superiority over the Channel, and "specialized" landing craft, the so-called LST's. The Germans had none of these advantages, meaning that their chances of success in a cross-channel invasion were less than 50-50.

Upvote:7

My comment above, as in pictures of thousands of pillboxes, was too flippant. Your question deserves a more serious answer.

There are two key things to consider, I think, when answering your question. One is that that the defence of the British Isles depended utterly on the Royal Navy. The Battle of Britain, considered pivotal in Britain's defence against invasion, was crucial because Germany could only even begin to contemplate a channel crossing if the all powerful Royal Navy could in part be neutralised by the Luftwaffe. And even then, in the case of absolute control of the air, most Germans still doubted they could overcome the Royal Navy and effect a successful invasion.

The second thing to remember, and here's where the pillboxes come in, is that Britain had just left most of its best equipment at Dunkirk. The cupboard was bare. Pillboxes were a quick and relatively easy way to establish a line of defences on the south coast.

I'm not sure whether anyone expected the pillboxes to work but they were a plan B, a very lowly plan B. Plan A was to stop the Germans in the channel, or dissuade them from the attempt, using sea power and air power. Which in fact is what happened.

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