Sealion compared to historical amphib assaults?

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Tsofian
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Sealion compared to historical amphib assaults?

Post by Tsofian » 05 Apr 2018 01:02

I'm interested in comparing Sealion to actual assaults. There are a lot of assault landings during WW2. Landings have a lot of factors, attackers defenders, fortifications, density, naval fire support, aerial fire support, rate of cross beach movement, terrain, weather, tide different.

What historical assaults were most like the plan for Sealion? What were most like it would like have been in reality (since no plan survives contact with reality?)

There are some things that make Sealion different than most other similar campaigns. One is the probably inability of the Germans to keep the Royal Navy away from the invasion beaches, if not away from the convoys on transit. The second is the possible inability of the Luftwaffe to gain and maintain air supremacy or even superiority over the beaches and the convoy transit routes. A third is the lack of NGFS.

What other assaults are most like Sealion and in what respects?

Thanks

Terry

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Re: Sealion compared to historical amphib assaults?

Post by Gooner1 » 05 Apr 2018 10:33

Dieppe 1942, but without the superiority at sea.

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Re: Sealion compared to historical amphib assaults?

Post by Knouterer » 05 Apr 2018 11:57

I agree that the Dieppe operation provides food for thought with regard to the chances of success of Sealion.

One of the weak points of the Dieppe plan was the lack of naval gun support, there were only a few Hunt class escort destroyers with 4" (102 mm) guns. The Germans would have had the exact same problem, nothing bigger than the 105 mm guns on a few M35 minesweepers (OK, apart from a few "Schwere Artillerieträger" on the far left flank, small steamers with a 127 or 150 mm gun).

Another notable fact is that all of the 4x4 vehicles landed (jeeps and Daimler Dingo scout cars) got stuck in the shingle on the beach. The German army in 1940 had very few all-wheel drive vehicles.
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Re: Sealion compared to historical amphib assaults?

Post by Tsofian » 05 Apr 2018 19:45

The M-35 minesweepers are an excellent ship. However they have two 4.1 inch guns, and those guns provide the only heavy flak weapons in the invasion fleet that are purpose designed naval mounts. The Flak 18 8.8 cm guns on the various ferry craft are improvised and their fire control doesn't have a stable element and they aren't designed to fire on the move. The M-35 vessels have around 200 rounds per gun, and those guns have three tasks-AAA, anti surface warfare, and NGFS. The crossing will take several hours and these weapons can easily run out of ammunition during that period. A single naval encounter could cause them to expend 25% or more of their ammunition. Even if they don't use all their anti aircraft ammunition on the crossing, which could also easily happen, they will still be expected to provide anti aircraft fire at the anchorages until the Luftwaffe batteries are established ashore.

I have not gotten a list of the number of improvised mounts for field and anti tank guns on assault ships and the converted gunboats, or their fire control and ammunition load outs. I also wonder how the shore parties would have called back for NGFS from any of the off shore assets that were potentially available.

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Re: Sealion compared to historical amphib assaults?

Post by Tsofian » 05 Apr 2018 19:48

Tarawa is also an interesting comparison. The problems of communications from shore to ships might be similar. At Tarawa US commanders were able to reroute assault groups away from some beaches that were too hot and to places where they might be more effective, or to hold up the waves if the needed to. I do not see how the Germans could have done this with the communications equipment and network they appear to have had available.

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Re: Sealion compared to historical amphib assaults?

Post by Kingfish » 06 Apr 2018 01:06

Tsofian wrote:There are some things that make Sealion different than most other similar campaigns. One is the probably inability of the Germans to keep the Royal Navy away from the invasion beaches, if not away from the convoys on transit. The second is the possible inability of the Luftwaffe to gain and maintain air supremacy or even superiority over the beaches and the convoy transit routes. A third is the lack of NGFS.
Probably the one thing that would have distinguished Sealion from other large amphib landings is how ill equipped the Germans were for such as undertaking. Their plan was to land 20+ divisions in three waves, with a significant portion being ferried/towed over the Channel in river barges.

Even assuming the Germans get the first waves ashore with light losses (a near impossibility) the destruction of many of these barges would doom the forces ashore, for the Germans had little else to supply and reinforce them.
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Re: Sealion compared to historical amphib assaults?

Post by Tsofian » 06 Apr 2018 01:27

Kingfish
I agree with this as well. If the campaign goes any length of time the battle will become one of attrition. Sooner rather than later the Germans will run out of surface warships and it will almost certainly be long before the Royal Navy does. At that point even if the Germans have air superiority during the day they still won't at night and the losses in barges will begin to get larger and larger. These are not only critical for the sustainment of the invasion force but are also required for the economy of Europe. The requirement for the transports to reload the assault craft several times makes them very vulnerable to any kind of surface attack.

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Re: Sealion compared to historical amphib assaults?

Post by Carl Schwamberger » 08 Apr 2018 19:06

Kingfish wrote:
Tsofian wrote:...
Probably the one thing that would have distinguished Sealion from other large amphib landings is how ill equipped the Germans were for such as undertaking. Their plan was to land 20+ divisions in three waves, with a significant portion being ferried/towed over the Channel in river barges. ...
In this context the only comparable Allied invasions were the combined operations of AVALANCHE, BAYTOWN, SlLAPSTICK in September 1943. Those had the object of placing over a dozen divisions ashore in a week or two. Op OVERLORD placed 20+ divisions in France in a couple weeks. The Allies could have put more ashore in a week in any of those operations, at the expense of their logistics support. But, whats the point in having 340,000 combat soldiers ashore without the 500,000 supporting men? I can't remember seeing how many thousands tons of artillery ammunition, fuel, horse fodder, small arms ammo, and supply transport, ect... the Germans were intending to move across the Channel in the next two or three weeks? Ten divisions equals 28,000 tons over the next 14 days just to sustain them in light combat. If its a heavy ongoing battle then 70,000+ tons is a good guess. More if any air units or large engineer contingents are moved to South England.

Any takes on if the supply for twenty divisions, or even ten could actually be sustained by the German sea lift at hand? What about after losses in barges and ships?

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Re: Sealion compared to historical amphib assaults?

Post by Kingfish » 14 Apr 2018 02:15

Carl Schwamberger wrote:Any takes on if the supply for twenty divisions, or even ten could actually be sustained by the German sea lift at hand? What about after losses in barges and ships?
No way the Germans could have gotten 10 divisions across, let alone landed and supplied. Just landing a division's worth of troops at select ports in (then) neutral Norway required nearly every warship in the Kreigsmarine's inventory. With fewer assets and an already alert Britain the possibility of repeating that limited operation would have been beyond German capabilities.
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Post by Sheldrake » 14 Apr 2018 10:17

Tsofian wrote:I'm interested in comparing Sealion to actual assaults. There are a lot of assault landings during WW2. Landings have a lot of factors, attackers defenders, fortifications, density, naval fire support, aerial fire support, rate of cross beach movement, terrain, weather, tide different.

What historical assaults were most like the plan for Sealion? What were most like it would like have been in reality (since no plan survives contact with reality?)

There are some things that make Sealion different than most other similar campaigns. One is the probably inability of the Germans to keep the Royal Navy away from the invasion beaches, if not away from the convoys on transit. The second is the possible inability of the Luftwaffe to gain and maintain air supremacy or even superiority over the beaches and the convoy transit routes. A third is the lack of NGFS.

What other assaults are most like Sealion and in what respects?

Thanks

Terry
Op Sea lion was to be a short assault crossing - like the raid at Dieppe and Normandy unlike Op Husky which was an assault after a long sea crossing.

Dieppe was a raid.It was not an invasion. Part of the aim was to force the German airforce into battle. The Royal Navy was reluctant to commit major units to the channel in daylight. The conventional wisdom is that Op Sealion might have been mounted but the landed force was unsustainable in the face of an undefeated RAF and RN. It might have been that the RN would rule by night and the luftwaffe by day.

However, this is a counter factual.We will never know how well the British would have fought in summer 1940. There are other parallels. The British were surprising losers in Crete in 1941 and in the Doedecanese islands in Autumn 1943. The Germans were able to improvise an assault force from far fewer naval assets and with bold use of air power. No one knows whether the Home forces would have fought better than Freyburg's men.

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Re:

Post by Kingfish » 14 Apr 2018 13:01

Sheldrake wrote:However, this is a counter factual.We will never know how well the British would have fought in summer 1940. There are other parallels. The British were surprising losers in Crete in 1941 and in the Doedecanese islands in Autumn 1943. The Germans were able to improvise an assault force from far fewer naval assets and with bold use of air power. No one knows whether the Home forces would have fought better than Freyburg's men.
To be fair their were factors in both Crete and the Doedecanese that wouldn't apply in Sealion, most notably the secure LOCs and an actual air force to counter an invasion.
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Re: Re:

Post by Sheldrake » 14 Apr 2018 14:54

Kingfish wrote:
Sheldrake wrote:However, this is a counter factual.We will never know how well the British would have fought in summer 1940. There are other parallels. The British were surprising losers in Crete in 1941 and in the Doedecanese islands in Autumn 1943. The Germans were able to improvise an assault force from far fewer naval assets and with bold use of air power. No one knows whether the Home forces would have fought better than Freyburg's men.
To be fair their were factors in both Crete and the Doedecanese that wouldn't apply in Sealion, most notably the secure LOCs and an actual air force to counter an invasion.
Air superiority was a prerequisite for a successful invasion. One scenario is that the Germans launched an invasion to provoke the RN and RAF to fight in the channel - using the army as bait. That would assume that after attrition battle the Germans could make good losses faster than the British - which is debatable.

The Deodecanese is an interesting one. In Oct-Nov 1943 the Germans should not have been able to amass air superiority in the Aegean. It is hard to see either the British or Americans mounting an assault with such unfavourable odds.

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Re: Sealion compared to historical amphib assaults?

Post by Tsofian » 14 Apr 2018 21:51

So the Germans will need to land 2,000 tons of supplies per day, in addition to the needs of any Luftwaffe forward deployed aircraft and follow on forces.

So they will need to be load 2,000 tons of cargo a day in the occupied ports and then capture enough working port capacity in England to unload 2,000 tons. It's unlikely that Dover will fall early, as the British have filled it with quality troops. In addition all the ports are well set up for demolition and there is a lot of artillery available. I really wonder how much the Germans would have been able to unload. I agree that they will be losing hulls every day to mines, surface attack, British submarines, operational issues, navigational problems, air strikes, artillery and who knows what else.

How much cargo capacity did the Germans initially have available? How much port capacity? Could they load 2,000 tons on the continent per day? If they could It would take at least day for the ships to get back across the channel, since they will need to be convoyed (at least until the German's run out of Escort vessels). If they ports can unload 500 tons a day that means that cargo ships will start stacking up in ports that may still be under artillery fire. I just don't see the math working out.

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Re: Sealion compared to historical amphib assaults?

Post by Knouterer » 15 Apr 2018 07:54

An interesting comparison could be made between Omaha Beach and landing zone B (between Folkestone and Dungeness) in the German Sealion plans.
Obviously there are very significant differences but there are interesting similarities too. Both involved a landing on a frontage of similar width by two infantry divisions, supported by a similar number of tanks (DD tanks in 1944 vs submersible/swimming tanks in 1940). Both beaches followed a gentle curve giving the defenders a good field of fire.

Most people would assume that Omaha beach was much more strongly defended, which may be true in terms of concrete, mines and other obstacles, but I do think the British defences by the end of September 1940 (the earliest possible date for an invasion) were stronger in terms of men and firepower per km. Of course, a direct comparison is difficult because the defences were organized and equipped very differently. The Britsh had about ten coastal defence guns of 5.5in and 6in calibre pointing out to sea, the Germans had none. On the other hand, the Germans had more guns, including a couple of powerful 88 mm Pak guns, pointing along the beach itself, which the British had not. Concerning indirect artillery support, the British had more and bigger guns within range, including four 9.2in (234 mm) railway guns.
It seems a safe assumption that the Germans, even if they somehow managed to get across in good order and on schedule, would have suffered at least as many casualties on S-Day as the Americans did on D-Day.

One of these days I'll work it out more precisely.
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Re: Sealion compared to historical amphib assaults?

Post by Tsofian » 15 Apr 2018 16:34

Knouterer wrote:An interesting comparison could be made between Omaha Beach and landing zone B (between Folkestone and Dungeness) in the German Sealion plans.
Obviously there are very significant differences but there are interesting similarities too. Both involved a landing on a frontage of similar width by two infantry divisions, supported by a similar number of tanks (DD tanks in 1944 vs submersible/swimming tanks in 1940). Both beaches followed a gentle curve giving the defenders a good field of fire.

Most people would assume that Omaha beach was much more strongly defended, which may be true in terms of concrete, mines and other obstacles, but I do think the British defences by the end of September 1940 (the earliest possible date for an invasion) were stronger in terms of men and firepower per km. Of course, a direct comparison is difficult because the defences were organized and equipped very differently. The Britsh had about ten coastal defence guns of 5.5in and 6in calibre pointing out to sea, the Germans had none. On the other hand, the Germans had more guns, including a couple of powerful 88 mm Pak guns, pointing along the beach itself, which the British had not. Concerning indirect artillery support, the British had more and bigger guns within range, including four 9.2in (234 mm) railway guns.
It seems a safe assumption that the Germans, even if they somehow managed to get across in good order and on schedule, would have suffered at least as many casualties on S-Day as the Americans did on D-Day.

One of these days I'll work it out more precisely.
It is very easy to say the German defenses were stronger based on the the thickness of the concrete. However the question is do defensive structures have enough strength to stand up to the weapons they will face? The German defenses had to survive off shore fire from guns up to 16 inch caliber but effectively lots of rounds from 5 inch 38 weapons from destroyers from close range being fired directly to destroy point targets. The Germans do have a very limited number of 15 cm guns and howitzers available on their makeshift gunboats, but these lack the fire control of the destroyers.

The survivability of Japanese defenses on Tarawa indicate that relatively "weak" defensive structures can still cause absolute havoc.

Zagola's book on Omaha indicates that the availability of 15cm field artillery was one of the critical factors in the heavy casualties. Much has been made of the Royal Artillery being forced to use 18 pdrs and other WW1 era weapons rather than the 25 pdr and other newer weapons. I'm not sure that matters at all. The WW1 era weapons were absolutely rock solid. They had a lot of available ammunition and there is no indication that the ammunition was in poor shape. The new weapons had advantages in range and mobility and in some cases lethality. That doesn't mean the guns fielded in 1940 would not have performed well enough to do the job. There is every indication that they would have been able to put killing fires on the beaches.

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