Reverse Sealion...

The original Sea Lion was wierd... but this has to be even stranger.

Baltic Project

I don't see it being very possible, but is there anything interesting to this story?

Here's some other stuff that came up when I had a look around.
John Fisher, 1st Baron Fisher
Letter: Fisher's plan to breach the Baltic - Opinion - The Independent

It's like a sort of Uber-Gallipoli isn't it?

What's even more crazy is that Churchill threw together a plan in WW2 called Operation Catherine, that involved the modification of 3 R-class BBs (adding extra armor plating), to send a major naval task force (IIRC consisting of a CV, 3 R-class BBs, and assorted CAs and DDs) into the Baltic to interdict iron ore from Sweden, and control the Baltic. Absolute lunacy, but he kept this up in the face of universal military opposition for 6 months during 1940.

David Floyd said:

What's even more crazy is that Churchill threw together a plan in WW2 called Operation Catherine, that involved the modification of 3 R-class BBs (adding extra armor plating), to send a major naval task force (IIRC consisting of a CV, 3 R-class BBs, and assorted CAs and DDs) into the Baltic to interdict iron ore from Sweden, and control the Baltic. Absolute lunacy, but he kept this up in the face of universal military opposition for 6 months during 1940.

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Really? Well I guess your right, operationcatherine.pdf (application/pdf Object)..... what was he thinking? At least Fisher was drunk at the time!

Mr Stereo1 said:

It's like a sort of Uber-Gallipoli isn't it?

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How about doing it in 1917 after the US has joined in the war? After all, after the US joining the war the Allies had an overwhelming naval superiority. A naval expedition to Denmark would cancel the U-boat threat as they would be concentrated against the expeditionary forces. Demands for amount of ground forces would be rather small. The Allies would have to lose very, very badly before naval balance would be threatened. In the meantime the expedited shipping of US forces and supplies to the Western Front would more than offset all this.

Actually, after it was certain that the Allies had an overwhelming naval superiority after US joining the war, what for were battleships being saved? For the next war? (of course some did fight in the next war...)

Would have triggered an immediate German invasion of Denmark in order to seal the Belts and the Öresund with land forces.

The HSF had their training grounds (gunnery and torpedo ranges) in the Baltic, so it would have been a home game for them.
If they were deployed, they would have been destroyed, but the GF would also have been much smaller afterwards.
And as the British used to say, Germany could afford to lose her fleet, Britain not.

But the war in the Baltic was fought with mines for the most part. Thus it is also thinkable that only small craft could be deployed, torpedo boats and mine layers.
These were very effective in keeping the vastly superior Russian Navy at bay.

rast said:

And as the British used to say, Germany could afford to lose her fleet, Britain not.

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I agree, but by 1917 GF + the Allied fleets were so vastly superior to German fleet that they could take very heavy losses eliminating the German fleet and still have enough fleet to defend Britain. However, at the same time U-boats were a deadly threat to Allied sea lines of communications,

rast said:

But the war in the Baltic was fought with mines for the most part. Thus it is also thinkable that only small craft could be deployed, torpedo boats and mine layers.
These were very effective in keeping the vastly superior Russian Navy at bay.

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As far as the Russian Navy goes, it shows that one should count not only number of ships to see what navy is superior and which one is not... But you're absolutely correct on importance of mines and minor craft. In the Baltic the access to Baltic itself as well as to Gulf of Riga, Bay of Bothnia and Gulf of Finland could be also closed by land-based coastal artillery which is another factor very hard to estimate.

In fact WW I was largely a war between minor naval units which did not show up in pre-war naval discussions and are not usually mentioned in post-war books about which dreadnought was more impressive than another. British trawler fleet, for example, proved to be a crucial asset for defense of Great Britain. That's why if there was a contest about most important warship of 20th Century an ocean-going trawler would definitely earn a place on the list.

I agree. However, I don't think the British were too keen on having the GF reduced - only to find that Washington had the bigger navy now.
The Baltic was too risky a water, one might get in, but getting out again was quite another affair. Basically, all ships sent in could be written off.

I think the thread title 'Reverse Sea Lion' is well chosen.

Even assuming the initial landings succeed, both Britain and Germany would have to divert forces from other fronts for this new theater of war, but Germany would probably have a far easier supply situation. Even if Britain's supply lines were straight as the crow flies, the distance from Germany's industrial centers to the Baltic coast is shorter than the distance from Britain's industrial centers to the same coast. Of course the British have to circumnavigate Jutland which makes their supply lines longer.

The Germans can load supply trains in the Ruhr district or Silesia and the trains will bring the supplies to a point perhaps ten kilometers or less from the frontline, most ot the rest is done by horse carts, and if the fronts solidify, by light railway.
But how can the British get their heavy equipment on the beaches? Mulberry harbors were certainly not invented yet, and I assume that amphibious craft with ramps were not invented either. Capturing a port intact is also very unlikely. Germany had Zeppelins and floatplanes for the naval reconnaissance role and the British landing force would probably already have been spotted in the North Sea, if not then while entering the Baltic at the latest, so there is no element of surprise.

World War One weapons technology generally favored the defence, at least until the appearance of tanks on the battlefield, and it is unlikely that the British can get these ashore.

Then one also has to consider whether the Danes would defend the approaches to the Baltic against the British. According to this post (referring to the situation in 1905, however), they definitely would, and they would not make it easy for the British.

You dare mention that Sea Mammal!

Well the Germans had a plan Fall J to occupy Jutland. Scheduled to go off OTL in 1917 or at an earlier practical date to coincide with another Fall N the occupation of Norway it never came off.

The neck of Jutland had been fortified on the German side during the war and the area the occupation of a Reserve Corps.

Denmark had mobilized roughly 50.000 troops spending most of their day digging field fortification but also setting up shore batteries on the coast of the Great Belt. Those batteries frequently drilled making target practice on sea added by observation aircraft of the Navy.
Add to this minefields in the three belts and a rather modern navy albeit a brown water one though suited to the shallow Danish waters.

Problem is would they use all this hardware against an Allied expedition?

During the war a British sub ran aground in Danish waters and when attacked were relieved by Danish navy units.
German sailors were several times interned by the Danes when their ships had run on a mine.

OTOH Denmark also hosted French and Russian POWs taken by the Germans. And the officers corps really didn't want to fight the allies.

But of course the politicians would demand at least an armed protest made against the Allies so expect something like an early April 9, 1940(waiting for Redbeard to come down on me! ) if the Allies come in force though. But with a ready Danish army and navy, ughhh. Its going to be bloody.