This is a rewrite of this question in an attempt to reduce its scope and bring it back within the sites guidelines.

I was writing a story set in an alternative history in which Nazi Germany occupies England in World war two after successfully conducting the amphibious landings code named Sea lion. This has been covered by others before me, but after some research I suspect that my assumption of a successful amphibious assault was totally unrealistic.

Considering the specific points noted below, can anyone make a good case for how the Germans might have successfully carried out an amphibious assault on England In the September of 1940 given the forces available to them at the time? Or is it reasonable to assume that operation Sea lion was just a threat that had no realistic chance of success because of the presence of Royal Navy rather than the RAF? Assume history was as we know it up until the end of August 1940.

Specific points

The massive superiority of the Royal Navy over the German Kriegsmarine.

The Royal Navy’s ability to patrol the English Channel at night almost at will and the presence of friendly agents in the invasion assembly ports making surprise all but impossible.

The very slow anticipated speed and very large size of the German invasion fleets with each transport towing two barges at 3 - 4.5 knots.

The navigational hazards in the straights of Dover such as the Verne and Royal Sovereign shoals, wrecks, minefields and strong tides and black-out.

The German intention to conduct the invasion on a moonlit night.

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    $\begingroup$ While not necessarily within the scope of the question - It's been proposed that if the Germans had pushed on Dunkirk and killed/captured the British Army, that the British may have surrendered without an invasion. That was a significant portion of their armed forces, and the morale loss would have been huge. $\endgroup$ – Andon Sep 23 '17 at 20:41
  • $\begingroup$ I think well-placed misinformation about when and where the invasion would take place could've helped landing a couple of troops in England. My guess is that if Germany had succeeded to invade Britain in some way, the war would've been over a lot sooner because of how spread out the German troops would've been. How long do you want them to occupy England? To realistically do this, one might have to completely change almost everything about the war. $\endgroup$ – Raditz_35 Sep 23 '17 at 20:51
  • $\begingroup$ @Andon Not in scope: true. British may have surrendered: true. Morale loss would have been huge: true $\endgroup$ – Slarty Sep 23 '17 at 21:56
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    $\begingroup$ To be successful in 1940, Germany must begin a major program of building and secretly storing large numbers of watercraft no later than 1937. England successfully used command and control integration against real-time submarine and air attacks, so any detected cross-channel surface attack seems likely to have focused quite a lot of defensive fire and incurred quite high casualties. $\endgroup$ – user535733 Sep 23 '17 at 21:58
  • $\begingroup$ @Raditz Re misinformation: I believe the Germans did attempt to do this (but I’m not sure of the details). I think the misinformation was supposed to involve an invasion in East Anglia on the basis that it was good tank country. A successful invasion, I suggest, must involve more than half the troops arriving in battle worthy state and the ongoing ability to supply and reinforce the bridgehead for at least a month. If the only way to accomplish this is to “change almost everything about the war” then the amphibious assault as planned was totally unrealistic $\endgroup$ – Slarty Sep 23 '17 at 22:19

10 Answers 10


My answer will focus on the question:

Is it reasonable to assume that operation Sea lion was just a threat that had no realistic chance of success because of the presence of Royal Navy rather than the RAF? Assume history was as we know it up until the end of August 1940.

The short answer is yes, Sea Lion was just a threat. The RAF and RN were too strong, few German officials (Hitler, reported, included) even thought it was viable

Opinions at the time:

Even among the Germans there was no conviction to the success of an invasion. With one of the Luftwaffe generals, Adolf Galland, claiming:

"invasion plans were not serious and that there was a palpable sense of relief in the Wehrmacht when it was finally called off"

Gerd von Rundstedt even claimed that Hitler himself didn't see the invasion as a realistic strategy but instead as a bluff to put pressure on a demoralised Britain once France fell.

In Churchill's memoirs he says:

"Had the Germans possessed in 1940 well trained [and equipped] amphibious forces their task would still have been a forlorn hope in the face of our sea and air power. In fact they had neither the tools or the training"

It is even believed that attempts to gather intelligence were such sloppy examples of spying that they were actually attempts to compromise the already disastrous plan.


The Royal Navy and Air Force made any plans to cross the channel difficult to say the least. Not only would the troops need to land in one piece but they would also need horses (as the German army was largely horse-drawn) and tons of supplies. Getting these across safely would either require a powerful Navy the Germans didn't have or for the British to consistently hold back from intercepting these supplies. Neither of these cases are likely.

This stretching of troops, resources and supply lines would also damage the war effort elsewhere - don't forget Germany was fighting this war on multiple fronts. For Germany to commit to this the chance they wouldn't face serious attacks elsewhere. Even if the Germans had successfully invaded their occupation would become a high resource drain.

  • $\begingroup$ “My answer will focus on the question” excellent! I agree with you. The tens of thousands of horses required in the original plans were an army fantasy based on lack of knowledge of the available naval capability. The only source of co-ordination and over sight was Hitler himself. One point of dispute – the Germans faced no other credible threat at the time. No Africa Corp till 1941 and no other significant European enemy. $\endgroup$ – Slarty Sep 25 '17 at 14:35

England starved to near submission first

(This answer must be completed with sources, edits are welcome)

A successful operation Sea Lion in September 1940, given history as-is up to August 1940 is not plausible, as other answers has pointed out. However, a scenario leading up to a successful invasion at a later date might just be possible, given a string of alternate history events.

Suppose Hitler had focused more on the western front and the middle east, less on the upcoming operation Barbarossa. Suppose also that admiral Dönitz had been given more resources for the "wolf packs", thereby being able to completely cut off Atlantic shipping. Add Bismarck escaping without serious damage from the Denmark Strait. Also add a more isolationist (or even sligthly pro-German) president than FDR in the US.

Then you have Britain effectively cut off from any imports. Keeping up repairs to defensive structures at the same rate that Luftwaffe destroys them without materials would be challenging. Food would be short, bringing morale down. Perhaps even to the point where Churchill would lose popular support. The Royal Navy was stretched thin even in real history. Without lend-lease and with supplies shipping essentially cut off, how long could it rule those waves?

Given that scenario, an invasion might actually have a chance...

  • $\begingroup$ An interesting scenario, although it would not have been feasible in 1940 as the Bismark was not fit for active service until the following year and I was specifically asking about scenarios “given the forces available to them at the time” rather than those involving reallocation of resources. But true A more isolationist president would definitely have helped $\endgroup$ – Slarty Sep 25 '17 at 8:32
  • $\begingroup$ @Slarty True, this scenario (esp given history as-is until aug -40) is not an answer if the invasion must happen at sep -40). It just might, however, be the basis for a successful invasion at a later date, after a near-complete blockade and the grinding down of the RAF and royal navy. $\endgroup$ – Guran Sep 25 '17 at 10:46
  • $\begingroup$ I'm not sure this approach is possible at all. At the height of submarine warfare, Britain was still commissioning more transports than were lost. With rest of commonwealth (Canada, Australia, India and others) mobilised, I do not think it was possible to starve Britain at all. Just like in WWI, it was only Germany that faced serious risk of resource starvation. $\endgroup$ – M i ech Sep 25 '17 at 12:43
  • $\begingroup$ @Guran Ironically one of the reasons the losses in the Atlantic were as heavy as they were was due to Churchill’s insistence on keeping a large number of Destroyers stationed near the channel due to the invasion threat. $\endgroup$ – Slarty Sep 25 '17 at 12:48
  • $\begingroup$ @Guran As many have mentioned above, this is highly implausible. It is interesting though, and as mentioned, could work at a later date. :) $\endgroup$ – A.G. Weyland Sep 25 '17 at 14:02

So to point the obvious solution: You don't go through English Chanel.

what's wrong with the ol'Viking routes? You have much more shipyards and port in Denmark and Norway. Most of the Royal Navy is in the Chanel so you can bottle them there with offensive units (you need transport and defensive to carry the attack on the ground). You have much wider coastline to disembark in Scotland than in England. Not to mention oil in North Sea that could be easily distributed to war effort.

The shortest way is not always the easiest or the fastest one. Imagine starting a campaign from Norway. RN trying to intercept the fleet is attacked near Calais by ships from Denmark. At the same time another "blitzkrieger" army is set to Exeter from Cherbourg-Octeville with a task to take Bristol and later Liverpool. The point is to take Devon, Wales and Scotland with a plan to pull out of them and attack on England. Leaving those regions "independent".

British Isles don't posses any natural sources Germany would want. So Fuhrer should want only to knockout the enemy, or cripple him enough so he posses no threat. Then he could focus and move resources to Western Front while fan the flame of uprisings in Scotland, Wales and Ireland.

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    $\begingroup$ Historically, the RN main base was in Scapa Flow in Scotland, making it easier to intercept the 'viking route'. The entire invasion fleet would be sunk at sea.. $\endgroup$ – Andrew Dodds Sep 25 '17 at 8:24
  • $\begingroup$ @AndrewDodds OP's set time to September 1940. In such time bracket and plan the attack on Scapa Flow would be postponed to stop Britain from strengthening the base. Or the attack would be coordinated with invasion. $\endgroup$ – SZCZERZO KŁY Sep 25 '17 at 9:05
  • $\begingroup$ The Germans would not have been able to stop the Home Fleet from leaving Scapa Flow as they had insufficient naval forces and Scapa Flow could only be attacked by unescorted bombers. $\endgroup$ – Slarty Sep 25 '17 at 9:34
  • $\begingroup$ @Slarty Yeah, that's the point. You don't stop them from leaving. You attack them there. As Germans did in 1939. With invasion plan on sep. 1940 they could postpone the attack and carry it with more ubots. $\endgroup$ – SZCZERZO KŁY Sep 25 '17 at 10:34

Fritz X

Simply, Hitler pauses after taking France, and decides to finish off the UK before starting with Stalin. Of course, a good choice would be become serious about the african campaign. Taking Egypt and the Middle East from the british means controlling the Suez canal and thus severing the ties between Britain and its overseas empire. With the moroccan coast in Vichy's hands (and a helpful spanish government in the Canary Islands) circumnavegating Africa is not an option, either. The ships have to go through the Pacific, then the Atlantic, or going through South Africa, then crossing the Atlantic westwards, going north, then crossing back eastwards. And now you have a very easy way to attack Soviet Russia from the South as well as the West, with the russian oil fields just a few miles from your panzer armies.

But even in that case, if the UK doesn't sues for peace, the RAF and the Royal Navy are a serious problem. If starving England is not enough, then you use your time to develop and enhance the Fritz X. Although, just like many of the "wonder weapons" of the nazi, it arrived too late, in too few numbers to be useful for the Third Reich, if it had been available in the early stages of WWII it could have made the Royal Navy to remain at the harbour for the whole war. Being the first operational anti-ship guided missile at a time were no effective anti-aircraft weapons were deployed on ships, it would have been a game-changer. WWII changed the rules of sea warfare, proving that ships were at the mercy of planes - even if planes were carrying just torpedoes or unguided bombs. With a quite precise guided missile on the highly effective Stuke dive-bombers, the Royal Navy would have sunk if tried to prevent the invasion.

  • $\begingroup$ You are correct to say that WWII changed the rules of sea warfare showing how vulnerable ships were to air attack. However in the summer of 1940 the majority of the war was yet to be fought and those capabilities were not fully developed. The Germans had no Fritz X or even an effective torpedo bomber at that time. Whilst even then air power was a serious threat to naval forces, the BEF was still rescued from Dunkirk by sea despite the loss of 6 destroyers and many other vessels and despite the ships being sitting ducks stationary for long periods and not manoeuvring at 30-40 mph in open water. $\endgroup$ – Slarty Sep 25 '17 at 9:02
  • $\begingroup$ The British RN attack on Mers El Kébir on the coast of French Algeria on 3 July 1940 may well have helped dissuade Franco from entering the war on the Axis side. Hitler was reported to have said he would rather have all of his teeth pulled out than undergo another meeting with Franco (Franco had been asked to join the Axis by Hitler but had stone walled). $\endgroup$ – Slarty Sep 25 '17 at 9:04
  • $\begingroup$ That's why I say "Hitler pauses after taking France". Germany's problem in WWII can be sumed in one: overreaching. They were trying to do too many things at the same time. Just as its armies were far too spread, so was its I+D and weapon research. They lacked a proper tank destroyer in 1940. They lacked long-range bombers. They lacked sea power. They lacked reconaissance aircraft. They were just unprepared for a war - Hitler didn't expect the UK and France declaring war because of Poland. Hitler should have just called a halt after the battle of France, then preparing thoroughly for Sea Lion. $\endgroup$ – Rekesoft Sep 25 '17 at 9:15
  • $\begingroup$ And as for Franco, he was a far better politician than he was a general. One of its biggest achievements was convincing the world that Hitler wanted him to join the Axis but he said no. In fact, Franco wanted to enter WWII, but he demanded the then-french Moroccoan coast for Spain. Hitler knew how devastated was Spain after the civil war and didn't want to compromise its pact with Vichy for the petty help an impoverished Spain could give. He was already carrying the italian failures on its shoulders to add another burden on the german forces. $\endgroup$ – Rekesoft Sep 25 '17 at 9:26
  • $\begingroup$ Britain had been impotent, backed down or retreated in Czechoslovakia, Poland, Belgium, Holland, Norway and France. And Hitler had convinced himself that the only option facing Britain was another armistice. He did not understand the mood in the country at that time. He very much did try to call a halt after the Battle for France but Churchill was not up for negotiating anything. Hitler “I can see no reason why this war must go on. I am grieved to think of the sacrifices which it will claim…”, Churchill “…and the dark curse of Hitler will be lifted from our age.” $\endgroup$ – Slarty Sep 25 '17 at 10:42

Decapitation and surrender

In light of the edits in the question..

In conventional military terms, Sealion cannot happen, and it cannot happen for several different reasons. Even if you remove the British fleet somehow, the Germans simply don't have the shipping to sustain an invasion, and don't have air superiority. Alternatively if you remove the entire RAF, the fleet can block the channel. And this is an opposed landing with bad geography and a prepared defense.

Not going to happen.

So.. decapitate. One day in late August 1940, Churchill is hit by a freak bomber (German tactics did include occasional lone bombers). This causes a leadership crisis in the government, and the re-emergence of the appeaser/peace faction. With a sudden loss of leadership at the highest levels, confusion reigns, and a rushed peace deal is made with the Germans, as part of which British units have to stand down and leave a demilitarized zone. The moment this happens, the Germans launch a sneak attack with every boat and transport plane they can lay their hands on. Completely demoralized and confused, the British surrender and are occupied - the surrender happening within a few days, because even in this scenario a sustained campaign doesn't work.

  • $\begingroup$ Churchill would have been a grievous loss to the British cause. It’s unclear to me what would have happened then, it would have depended on who got into power. I suspect that Operation Sea lion would have had even less chance of happening then as Hitler would have been very keen to wait and see what pressure he could put on the new administration rather than try a risky channel crossing. That said this is probably the best answer to date, $\endgroup$ – Slarty Sep 25 '17 at 11:04


Without air or water superiority, why not go by land?

The service tunnel connecting England with the Europe took two years or so to complete. It may have been built with better technology granted, but it was also built to a higher standard, wherein the Germans could produce a hasty short-lived tunnel. Some, perhaps dubious, estimates even being placed at 16 months

With a land route available, a naval and air distraction could help conceal the movement of Germans tanks. Once they arrive on the island the Germans can exercise their blitzkrieg tactics, focusing on seizing air and naval bases.

There are clearly a lot of issues with this plan:

  1. Concealing the construction of a tunnel
  2. Constructing the tunnel in a limited time-frame
  3. Moving troops without being noticed
  4. Protecting the tunnel until the sea/air bases can be dealt with

The upside is the Germans get to do what they do best, Blitz. While perhaps not the most realistic plan, its one you have fun with, and does get around some limitations the Germans faced.

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    $\begingroup$ Imaginative, but I don’t think it would have been practical in 1940 as it would have taken too long to build, if it could have been built at all. Also a few realy large depth charges detonated on the sea bed above the tunnel would have destroyed the whole thing in minutes. $\endgroup$ – Slarty Sep 25 '17 at 14:20
  • $\begingroup$ Well I addressed the concern around time (with the lowest estimate at 16 months), but if you have a specific time frame in which you want your events to occur by you should also specify that in your question. $\endgroup$ – Firelight Sep 25 '17 at 14:52
  • $\begingroup$ As for the chance of collapse, they would have to be aware of the tunnel to target it for one. But given its a war the possibility of stray charges, neither of us can say with certainty without looking into it further what forces the tunnel could withstand. There is maybe 60 meters of earth and rock between the channel bottom and the tunnel. The Channel Tunnel itself was designed to be earthquake resistant (some people say proof but that's probably a tad too confident) $\endgroup$ – Firelight Sep 25 '17 at 14:54
  • $\begingroup$ They would have been aware because of the huge effort involved, the vast amounts of spoil excavated, aerial reconnaissance and the existence of many chatty disgruntled Frenchmen. It’s true to say we don’t know for sure. But 27 tons of amatol did this during WW1 youtu.be/Zw2vABLJFQk creating a hole 30 meters deep and 100 meters wide. If that sort of device was detonated with an overburden of 45 m of seawater directing the explosive force downward I would not fancy being in the tunnel. $\endgroup$ – Slarty Sep 25 '17 at 15:30


The key here is preparation.

That means that Germany has studied the problem AND has developed some amphibious capability BEFORE the battle of France. Historically, this didn't happen because they never expected France to fold so quickly - after all, prior to the disastrous Dunkirk campaign, the British/French/Belgian forces outnumbered the Germans and had better equipment.

But in our alt-history, Germany has an invasion fleet ready by 1940, with a fleet of landing craft capable of taking several divisions and assembled in total secrecy; Germany has also invested more in naval forces, having more destroyers and light craft than in 'real' history.

And it is not a September invasion. The fall of France happens at the end of June; by September, Britain has had several months to recover and prepare for invasion - building fortifications, re-forming divisions saved at Dunkirk, raising the Home Guard, and generally re-arming. But at the end of June, it's all still in chaos.

So - Germany hits at the end of June/start of July, with a massive air attack and sufficient invasion shipping to rapidly get 3-4 divisions ashore, plus paratroops. At this point in history there are practically no organised land forces to oppose them. The narrow part of the channel falls into German hands, with the German naval forces being just strong enough to hold off local British forces (historically several dozen destroyers). As a dramatic twist, perhaps we have Churchill and other senior politicians killed in an air attack. A decapitated government surrenders in panic, before the British fleet from Scapa Flow can close the channel crossings. It has to happen as early as possible and as quickly as possible; the more time the British have to prepare the less likely the invasion is to succeed.

  • $\begingroup$ Remember "given the forces available to them at the time". How could the Germans have used the forces available to them at the time to make the attack? $\endgroup$ – Slarty Sep 25 '17 at 9:40
  • $\begingroup$ I have edited the question slighty to make this clearer. $\endgroup$ – Slarty Sep 25 '17 at 9:45

Because its hypothetical - the German Luftwaffe was able to fend of the Operation Catapult - that their former ally wanted to kill them were as their former enemy protected them might be enough the french fleet surrenders to Germany and bolster their assets. Together with the strong Italian Navy it should have been enough to make Axis and English Navy equal.

As a addition Hitler doesn't give the "hold" order at Dunkirk and the Germans overrun the beach capturing most soldiers. This would have been a moral blow to the fighting will.

But without the support of the french and Italian Navy plus the low range of the German Luftwaffe the invasion would have been indeed impossible.

An alternative might have been an invasion of Ireland and a "blockade" by Submarines to give transport ships the ability to send supplies and troops.

About the realism - if Sea Lion would have been a "real" option - German would not have tried to broker a ceasefire since 1940.


As the other answers have shown, it's not very realistic that Operation Sealion itself could have succeeded. But it might have been possible with Godlike prescience/military intelligence, at least to land a significant number of troops (without armour), which would open up other options. In this scenario, the Dunkirk excavation has failed spectacularly, and in addition the Axis powers have captured the French and Dutch navies.

The combined Axis fleet take control of a narrow portion of the channel for a period of five to six days. This would be achieved via distraction (somehow diverting a large portion of the Home Fleet to Scandinavia or Iceland), sabotage (somehow blocking RN ships from leaving from Scapa Flow) and the element of surprise. During this time the Germans use their small craft to ferry ~200,000 soldiers to the south of England. I don't have sufficient information about the size and capacity of German small craft, but a rate approximately the same as the real Dunkirk evacuation seems plausible. The RAF is an issue during this period but the number of troop losses is not greatly significant due to the use of speed and smokey cover.

  • $\begingroup$ Problem being Hitler was more gambler, improviser and bluffer than God like military intelligence. Unfortunately Dunkirk has already happened as the questions Assumes history was as we know it up until the end of August 1940. “somehow diverting a large portion of the Home Fleet to Scandinavia or Iceland” does not sound likely given the expectation of an invasion.Navy estimates 165 steamers, 390 tugs, 140 trawlers, 120 motor coasters, 1130 barges and 1500 motor boats required. Speed estimates 3-4.5 knots. The RAF and the Luftwaffe play no significant roleas they can hardly hit a city at night. $\endgroup$ – Slarty Sep 25 '17 at 18:53
  • $\begingroup$ Of course, as I said none of this is likely. You're asking for hypothetical scenarios, no? > Unfortunately Dunkirk has already happened Fair enough, I missed that in the question. Though it doesn't change my answer. $\endgroup$ – K. Morgan Sep 25 '17 at 22:57

Most of the Royal Navy gets destroyed by a massive storm.

This famously happened to not one but two Mongol invasion fleets sent to invade Japan. The Romans also managed to lose their fleets to storms several times.

It was less likely to happen to the Royal Navy due to the fact that they had radios and weather forecasts, but they didn't have satellites or computers so it is still plausible that they could be blindsided by a storm.

A storm could also hit the UK itself and destroy planes and infrastructure, gifting an easy victory to Hitler, should he be ready to seize the opportunity.

Of course Hitler would still need a lot of ships, but he might be able to scrounge together civilian vessels and Japanese/Italian vessels to make it happen.

  • $\begingroup$ A good try. But I think the RN was too widely spread and were fairly good at dealing with storms and bad weather. Storms hitting the UK might do some damage but it would more likely be a danger than a benefit if you want to move 1000's of river barges. Hitler did scrounge civilian vessels that’s where the barges came from and the tugs. Japan was realistically too far away and Italian shipping would have been (and in fact was) very vulnerable to the RN fleet in the Med (eg Crete and Taranto) and the Atlantic $\endgroup$ – Slarty Sep 24 '17 at 2:06
  • $\begingroup$ The Royal Navy could be concentrated if they thought a major engagement was going to happen. For instance, if the Kriegsmarine was intercepting convoys and the Royal Navy was trying to intercept them. Also, Hitler could not realistically organize the invasion faster than a couple of weeks so the barges would be safe from the storm and Japan would have time to get them some ships. Italy might have trouble getting ships past Gibraltar but could resort to sending them through the Suez Canal and going around Africa. $\endgroup$ – James Hollis Sep 24 '17 at 10:51
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    $\begingroup$ Just to illustrate the scale of the problem The Royal Navy Home fleet consisted of 3 battleship, 2 battle cruisers, 11 light cruisers and 80 destroyers all in home waters, plus another 10 cruisers and 52 destroyers in the Atlantic. The Germans had 2-3 cruisers and 10 destroyers, all other heavy units either being under repair after the Norway or were not yet operational. In 1939 German Grand Admiral Raeder had said “The surface forces are so inferior in number and strength to the British fleet that, even at full strength they can do no more than show that they know how to die gallantly.” $\endgroup$ – Slarty Sep 24 '17 at 18:47
  • $\begingroup$ Although Egypt became independent in 1922 the British retained control of the Suez Canal until 1952. I don’t think they would have been happy with letting the Italians (or the Japanese) use the canal at that time. $\endgroup$ – Slarty Sep 24 '17 at 18:48
  • $\begingroup$ Yeah, I know it's hard. That's why you only have one answer and that answer is an act of god. I think a more realistic Axis victory can be achieved if it does not include Operation Sea Lion. For instance, if everything went wrong on D-day and most of the Allied army got killed or captured. Or Hitler might convince Hirohito that attacking the USA was a really bad idea. That sort of thing would make it easier for the Axis powers to build up their navies to the point where invading Britain was realistic. It would be a lot later than 1940 though. $\endgroup$ – James Hollis Sep 24 '17 at 22:25

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