Operation SEALION is one of the great red rags of alternate history. It's been tried many times and at different places, but it's been generally agreed that executing the plan at the time (fall of 1940), in that particular strategic situation and with the means at hand was a very bad idea. With that in mind I've tried to come up with a few basic ways to make the idea slightly less bad.
The purpose of this list isn't to be exhaustive, and I'm aware that there are most likely a myriad of other, more specific factors that play a role. It's not about operational details and specifics but more about the general line of approach to make a German victory more plausible (FYI, plausible does not mean likely or guaranteed). This list is in no way exhaustive, and I'm more than aware that some points hinge on a lot of factors out of direct control working exactly as hoped for. As such, consider this more an approach to minimize risks and maximize the chance of a potentially successful outcome. So, with this out of the way, let's consider SEALION.
This one is self-explanatory. An operation as massive as an amphibious invasion of another country demands the creation not only of the necessary transport capacity but also the establishment of supply stocks & channels as well as working out routines to support the troops over that very specific gap once they are in the field. That means dedicated landing craft in significant quantities PLUS backup landing craft (for example converted barges for calm seas) PLUS aerial transport capacities PLUS supply stashes in northern France & open railroad connections into Germany.
This is imminently possible for Germany to achieve within a comparably short period of time (less than a year). It has the industrial backbone and - due to probably the biggest inland navigation in Europe sans Russia - the necessary manufacturing infrastructure. The main problem here is that the necessary interference into these "civilian" sectors in the time frame during which a German attack against the British mainland was plausible is not a given due to the "short war" vision the Nazi regime still propagated at the time. But the technological and administrative know-how certainly does exist.
a) The railway connections between northern France and the industrial heartland of Germany are adequate to support forward operations, being able to use the well-developed Dutch, Belgian and French networks to build up stocks and quickly bring in supplies from the home front.
b) Germany's large number of river ports and its established use of its main rivers for commercial purposes give it a wide range of inland shipping berths capable of producing vehicles in the <1,000 ton range. A dedicated building program of seaworthy landing crafts would be able to provide a large number of crafts within a comparably short window of time.
c) The Wehrmacht's super-heavy and railroad artillery available in the envisioned window of opportunity consists of at least 60 pieces greater than 20.3 cm with a range of more than 25,000 meters. German radar on the Channel coast can track ships. Use both to prepare a "safe" corridor for the invasion fleet (the move would naturally mean a change away from the originally intended wide front approach). This represents an qualitative and quantitative increase of what Germany planned and did do historically.
2. Concentration of Forces
No wide-front approach (as envisioned by the original SEALION plans) will ever be feasible with the resources even a well-prepared Germany might have. It's just not possible to land forces between Lyme Regis in the west and Ramsgate in the east and expect not to lose significant portions of them already on the voyage. The wider the front the longer the journey the greater the risk of premature detection and interception. Attacking on such a wide front is like sending the RAF, RN and Royal Army a written invitation. It favors the logistics of the defender in every conceivable way. Secondly, such a wide dispersal of forces makes it very difficult to
a) overwhelm local, dug-in defenders and
b) form a Schwerpunkt to counteract British efforts to bolster defenses at the landing zones and strike deeper into south-east England proper.
In essence that means for the Germans to attack on a limited front, ideally beneath the umbrella of CAS and coastal artillery and within a zone where the Luftwaffe in general can claim and extensive operational duration. Landing zones proper should be in an area between Dungeness and Dover, at a maximum between Ramsgate and Eastbourne.
It also means that the invasion force would form an army of its own, meaning it wouldn't consist of elements of several armies (three in the historic case - 6th, 9th and 16th), thus making it easier from a command and control point.
3. Dispersal of Enemy Forces & 4. Deceit
Now we're getting into more troubled waters. Everything mentioned so far was ultimately hinging on the Germans simply doing something. Meaning, no specific reaction on the side of the British was needed to get it underway. Any "Sealion" that is prepared and conducted simply as a military operation is doomed to fail. To even have a plausible chance a large number of factors have to act in concert, with diplomatic and covert operations starting weeks and months before the act.
Points 3 and 4 are closely related. German behavior, German actions elsewhere, German INaction, even matters Germany may have no control over whatsoever have a part in this. Some openings might be these:
- Put the focus on the Mediterranean, drawing in additional Royal Navy and British Army units. The enemy has to be occupied enough to believe he is dealing with a significant part of your overall strength.
- Act militarily passive against Britain (the island) itself: take a purely defensive stance, limit raids and submarine warfare.
- Due to a passive stance allow for RN vessels to be withdrawn prematurely to deter the Japanese.
- Convey the lasting (i.e. for at least several months) impression of desperately wanting to seek peace by using non-aligned and not yet hostile nations to approach the Empire's embassies.
- (20/20 hindsight) Order your spy network to feel out the mood for war/peace in Great Britain. Since 99% of your spies are actually double agents turned by MI5 Britain will have to assume you're seriously interested in a cessation of hostilities.
- Pre-invasion (app. one week): launch surface raid into the Atlantic to draw away some of the RN's capital ships. Give them a necessary incentive to follow you in strength.
Or put simpler: concentrate your enemy's aerial and land strength elsewhere, encourage him to disperse his naval strength as much as possible.
5. The Element of Surprise
This is really just the Schlieffenplan dynamic all over again. German transportation and mobilization has to be fast enough to outpace the British response. Troops and equipment need to be carried to the harbors fast enough to avoid British detection as long as possible, and they have to get there while British forces on land, sea and air are largely engaged elsewhere. Additionally to much of points 1 to 4 having to function this also means that during the time of preparing the whole operation the Germans will have to optimize their logistics network between Germany, the Low Countries and Northern France.
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Well, and that's that. Tell me what you think. As I said at the start, this list is far from exhaustive so don't get all mad because I didn't mention that one specific point you had in mind. If you like, add to the list yourself.
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Sebastian P. Breit is the author of the alternate history novel Wolf Hunt. You can find news, reviews, and commentary on all matters regarding WW2 on his blog, The War Blog, and follow his writing progress on his personal website.