What If - D-Day In Reverse

It’s time for the big ‘what if’!

We just discussed the ‘what if’ idea of how Germany might have been able to stop the Allied D-Day invasion.  In addition to what we talked about, there was one other possibility to stop the invasion and that would have been for Germany to invade England, first.  In fact, Germany formulated plans for exactly that operation, calling it Sea Lion.  Most post-war analysts and historians do not believe the plan could have succeeded and, indeed, Hitler’s own military leaders expressed little support for the idea.  Still, could it have worked?  Sounds like another ‘what if’!

As it happened, the invasion was war gamed in 1974 at the Royal Military Academy Sandhurst.  Wiki has a good write up on the event and it makes for fascinating reading. (1)  Let’s examine Sea Lion as a ‘what if’ and take a look at how the war game played out.

Let’s start by looking at the war game results.  To put it succinctly, the game demonstrated that the initial invasion wave was readily able to cross the channel and land.  However, the follow on waves were decimated and the invasion died due to lack of supplies.  The German forces in England were defeated and surrendered.  As I said, Wiki has a nice description of the game and I won’t make any great effort to repeat it but there are a few items that are noteworthy.

The game was heavily biased against the German effort and in favor of the English.  This started with the initial inclusion of a map of the landing area which instantly triggered a massive surge of units straight to the area as opposed to maintaining the landing site uncertainty that would have accompanied a real invasion.  We saw the negative impact that site and timing uncertainty had on German defenses and there is no reason to believe that the same uncertainties wouldn’t have negatively impacted English defenses.

The German cross-channel transport vessels were severely underrepresented in the game, leading to limited troop and supply transport.  From the Wiki article,

The Germans had only converted river barges available as transport ships. Not a great deal was known about the invasion fleet at the time of the wargame. This represented a gross simplification relative to shipping plans discovered later, which involved nearly 4,000 vessels, including 150 merchant ships and 237 light or auxiliary close escorts, in four invasion fleets.

The invasion fleet naval assets were limited to some E Boats, U-Boats, and destroyers.

The British Home Fleet was sent south to interdict the invasion force contrary to historical intent.  From Wiki,

In real life, both Admiral Charles Forbes, commander of the Home Fleet, and Admiral Dudley Pound, First Sea Lord, said they would not send capital ships into the Channel unless the Germans did so, too.

The first two days of the game included weather conditions which prevented the German invasion fleet from launching.  Nonetheless, the previously mentioned map issue which revealed the landing site enabled the English to spend two days surging ground forces to the future landing site secure in the absolute knowledge of the site’s location.  Thus, the English had a two day start on the game.

The initial assault wave was able to land relatively unimpeded and managed to advance 12 miles inland and captured the ports of Folkestone and Newhaven.

German minefields shielded the invasion force.

The Luftwaffe conducted bombing attacks on London instead of directly supporting the assault forces.

The game was decided when the German’s second assault wave was intercepted and destroyed by a Royal Navy (RN) force of 17 cruisers and 57 destroyers.

Clearly, the game was heavily slanted towards the British.  Despite this, the initial assault wave made it ashore in good order and achieved some degree of success.

Now, let’s ‘what if’ the concept the right way and see if it could have succeeded.  Of course, being a ‘what if’, we wouldn’t invade Russia, thus doubling our available resources!

We need to start with defining the goals of an invasion and there would be two main goals. 

1.  To seize a port for follow on unloading of troops, supplies, and equipment.  Only a functioning port can provide the volumetric throughput of supplies necessary to support a large scale invasion.  Depending on a detailed study of available resources, seizure of a second port would be a desirable goal, as well.

2.  To seize an area suitable for an airfield.  This could be an existing airfield or just an open flat area that could be quickly converted to an airfield.  The purpose of such a field would be to allow critical supplies to be flown in and to allow local staging of the Luftwaffe rather than having to sortie from mainland Europe.  Local staging would enhance fighter cover and allow effective close air support by enabling aircraft to launch, attack, and land to refuel and rearm in short cycles.  Additional fields would be developed as the invasion progressed.

To accomplish this, our version of ‘what if’ starts out with many of the aspects discussed in the previous post and include:

• Refocusing the U-boat effort on sealing the northern approach to the English Channel, hunting British cruisers and destroyers, and bottling up the Home Fleet.
• Extensive laying of minefields at both ends of the channel and in lanes protecting the invasion fleet’s approach routes.
• Use of the Luftwaffe to destroy bridges, railways, and roads that would be used to move British reinforcements to the landing area.
• Use of the Luftwaffe to hunt British cruisers and destroyers.
• Co-ordinated use of the German battleships and heavy cruisers to screen the invasion fleet from British cruisers and destroyers.
• Use of E Boats to screen the German naval force.

With those measures in place, the actual assault would consist of the following operational steps,

• Airborne assault to secure the selected port.
• Airborne assault to secure the selected airfield.
• Amphibious assault to support the port seizure and isolate/screen the port from counterattack.
• Amphibious assault to support the airfield seizure.

Students of history will note the similarity between this operational plan and the Allies D-Day plan.  Many people think the D-Day assault was all about pushing troops across the beach and then straight on to Germany but the real purpose was to seize ports for the critical follow on supply effort which was the only way the subsequent large scale European combat could be supported.  The actual D-Day landing was all about seizing the ports.

Having laid out the goals, plan, and methods, we are now led to ask, would it have succeeded?

The wargame, even heavily slanted towards the British, demonstrated that the initial assault wave would have successfully landed and moved inland.  In our ‘what if’, we’ve enhanced the chance of success with more numerous, more substantial, and specific measures aimed at isolating and screening the invasion fleet.  Thus, there is every reason to believe that the initial assault would be quite successful.

Recall that the Allied D-Day assault landed in the teeth of extensive fortifications at the beach.  England had no such defenses, never believed an invasion was a real threat, and had no plans to fortify beaches.  There is every reason to believe the assaulting forces would have been able to land and move inland with only minimal resistance.

Airborne forces always enjoy initial success in terms of landing.  The question becomes whether they can assemble and organize once on the ground to the extent necessary to enable them to become combat effective and achieve their objectives.  As seen by the Allies’ D-Day efforts, the airborne element did succeed, though at a cost.  The Allied airborne effort was hampered by landing dispersed in somewhat featureless and difficult terrain which made assembly and subsequent effective combat problematic.  I would submit that landing an airborne force in and around a port city would be far more practical and easy.  Orientation of the forces, once on the ground, would be easier because a city is full of recognizable landmarks and the confusion factor for the defenders is immense.  I would aim a portion of the airborne landings directly on the port facilities and the remainder in and around the city to screen the port.

In the game, a port was seized.  Thus, there is every reason to believe that the initial port seizure objective could be accomplished quickly and easily.

The same reasoning applies to seizure of an airfield area.  Being, presumably, out in the country and isolated, an airborne landing and follow up support from amphibious troops would almost certainly ensure the successful seizure and establishment of a functioning airfield.  Thus, the assault would benefit immensely from the rapid establishment of a local airfield for fighter cover and close air support.

Where the game failed for the Germans was the second wave was intercepted by British cruisers and destroyers and completely destroyed.  This resulted in the initial force being ‘starved’ of supplies and the invasion died out.  It is no great surprise that the entire assault hinges on the follow on effort.  This is the logistics portion of war that ultimately determines military success or failure.  The measures we’ve outlined here should have been sufficient to ensure the success of the follow on supply effort.  That being the case, the entire assault would have had a fair chance of success. 

The importance in this ‘what if’ of Germany not attacking Russia cannot be overstated.  Being able to double the resources available to be brought to bear against England would have been incalculably beneficial.

We see, then, that the concept of an invasion of England was feasible and would have had a fair chance of success.  However, it would have been necessary to gear the entire German war effort toward this goal.  From the beginning, the Germans would have had to have been working toward this goal by not squandering U-boats and their surface ships, not attacking Russia, working to lay minefields and isolate the English channel, etc.  In other words, they would have needed a strategy on day one of the war that had this goal in mind. 

The importance of a coherent strategy cannot be overstated and offers a lesson for us, today.  What is our strategy towards Russia, China, Iran, and NKorea?  We haven’t got one.  How can we expect success, then?  But, I digress …

Had Germany been able to successfully invade England, how would the war have progressed beyond that point?  Would the US have prosecuted a war against Germany without England as a base of operations or would the US have attempted to negotiate a peace settlement of some sort?  If the US had opted to continue the war, would Africa have become the base of operations?  What role would Russia (not having been attacked by Germany) have played, subsequently?

What if?

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(1)Wikipedia, “Operation Sea Lion (wargame)”, retrieved 11-Mar-2019,

https://en.wikipedia.org/wiki/Operation_Sea_Lion_(wargame)

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