Why couldn't the Germans build an underwater tunnel to Britain?

[Tom from Cornwall]

Despite the above caveats, the AHF community did not respond in the open spirit of inquiry in which our questions arise

It might be of interest to those with an open spirit of inquiry to know that the British Chiefs of Staff Committee considered the possibility of the Germans building a Channel tunnel - see note in COS Committee papers for December 1942:

https://discovery.nationalarchives.gov. ... /r/C387289

This can be downloaded for free at the moment - you just need to register with the UK National Archives and then download away!

The paper I noted (in passing!) is No 458(42) - 19 December 1942 - POSSIBILITY OF A GERMAN CHANNEL TUNNEL AND STEPS WHICH CAN BE TAKEN FOR ITS DETECTION. Minute by the Lord President.

I haven't specifically looked for any references to possible Channel Causeways but given WSC's relentless spirit of enquiry I'd be quite surprised if he didn't mention it in any of his "nagging and pestering" minutes to the Chiefs of Staff about preparations for an invasion in the opposite direction. He definitely talked about causeways that would float up and down with the tide...and as a British schoolchild of a certain age he will certainly have been steeped in the mythology of King Canute.

Regards

Tom

[Rob Stuart]

Wondering how the long term strategy of building a tunnel would tie in with the German notion of short sharp campaigns i had a look at the Wikipedia article to see just how long it took to build the tunnel we have now. Started in 1988 and opened in 1994 which is about as long as the war lasted but there is an interesting note in the wiki article that says an officer from the "Directorate of Miscellaneous Weapons Development" calculated that the Germans could build two tunnels within 18 months using slave labour.

What kind of tunnels could be built in 18 months? It would of course not be sufficient to build tunnels wide enough only for columns of infantry to march through. They would need to be able to accommodate tanks, half-tracks pulling artillery, engineer vehicles loaded with bridging equipment, trucks carrying ammo, fuel, rations, mines, barbed wire, field telephone cable, etc. And if the tunnels are only wide enough for a single column of such vehicles, what happens if a Mark IV Panzer breaks down in the middle? How do you get a recovery vehicle to it to tow it away? Also, how do you remove all the exhaust fumes so that your troops don't collapse from carbon monoxide poisoning?

[Sheldrake]

I started reading this

Could the Germans build a 20-mile tunnel? Yes. Could they build the last mile without being drowned/blown-up? Almost certainly no unless the British don't notice the digging and excavation of the Britain-side exit until a substantial force has debarked, which seems unlikely.

I thought - I know the answer. The Germans use a vaulting horse to hide the tunnelling...

Then I read this...

Partially filling in the Channel allows Germany to approach the English coast to within field artillery range by linking up with the shallow ridges in the English Channel ("Varnes"), which can be easily filled over.

and I had to conclude that potential for satire had already been exhausted...

[TheMarcksPlan]

I thought - I know the answer. The Germans use a vaulting horse to hide the tunnelling...

What a wonderful place AHF is.

[Wat Tyler]

Wondering how the long term strategy of building a tunnel would tie in with the German notion of short sharp campaigns i had a look at the Wikipedia article to see just how long it took to build the tunnel we have now. Started in 1988 and opened in 1994 which is about as long as the war lasted but there is an interesting note in the wiki article that says an officer from the "Directorate of Miscellaneous Weapons Development" calculated that the Germans could build two tunnels within 18 months using slave labour.

What kind of tunnels could be built in 18 months? It would of course not be sufficient to build tunnels wide enough only for columns of infantry to march through. They would need to be able to accommodate tanks, half-tracks pulling artillery, engineer vehicles loaded with bridging equipment, trucks carrying ammo, fuel, rations, mines, barbed wire, field telephone cable, etc. And if the tunnels are only wide enough for a single column of such vehicles, what happens if a Mark IV Panzer breaks down in the middle? How do you get a recovery vehicle to it to tow it away? Also, how do you remove all the exhaust fumes so that your troops don't collapse from carbon monoxide poisoning?

I perhaps should have said that i found the idea of an 18 month build for two tunnels something of a fantasy . Just noting the wiki article. Otherwise i agree with what you've written. If anything i would think building the majority of the tunnel is the easy part , but how does anyone finish the British end of such a tunnel without being noticed and giving the army time to bring up all their big guns? Nonsense really.

[daveshoup2MD]

I realize this is probably the stupidest question ever and wouldn't work for many reasons, but I'm asking so I could potentially get more detailed information as to why.

The first underwater tunnel was constructed from 1825–1843, so the technology was there. I am definitely not an expert in this kind of engineering (or engineering in general) but could they secretly build a tunnel to transport an army? How does a construction project like that need to be coordinated?
It looks like Churchill wanted to construct a channel-tunnel at the time, but nothing came of it.
https://en.wikipedia.org/wiki/Channel_T ... _proposals
The Channel tunnel in our time line was constructed from 1988-1992 (4 years) but if the Germans had put enough cash and resources into it I don't see why they couldn't build it ahead of schedule.

Because there's no way to "secretly" build a large civil engineering construction project in wartime in a theater where aerial reconnaissance is a daily, if not hourly occurrence, and and human intelligence was entirely on the Allied side of the ledger? Plus, of course, the Allies had significant penetration into German planning, in terms of both cryptoanalysis and human intelligence?

And, of course, the geologic, geographic, hydrographic, and engineering problems for a channel tunnel are very significant. There were (basically) two ways to dig tunnels in the mid-20th Century; trenching it or tunneling using pneumatic shields. Trenching across the channel is a non-starter; pneumatic shield tunneling would be technically possible, but that's like saying building a dam at Gibraltar is technically possible ...

Take a look at the Holland Tunnel, built in the US in 1920-1924 by pneumatically pushing cylindrical shields through the Hudson River's bottom (Beamont's idea from the 1880s, basically, so 40 years of technological maturation). The shields not only dug through mud but also served as the shell beneath which the actual tunnel walls (built of iron rings filled with concrete) were constructed. Two shields were used—one began on the New York shore and the other on the New Jersey shore. They met in October 1924. The north tube is ~8,600 feet (2,600 meters) long and the south tube 8,400 feet (2,550 meter) long. The roadway is 20 feet (6.1 meters) wide and reaches a maximum depth below mean high water of 93 feet (29 meters).

The Hudson River is ~8,600 yards across, and it took roughly four years in peacetime, with excellent access to skilled labor and a supply chain; the channel tunnel is 31 miles long, and in 1940, northwestern France is not exactly comparable to the NYC labor market, and there's no friendly rivalry between two teams on the same project, is there?

This is worth reading, for a general history of heavy civil engineering in the 20th Century:

https://view.flipdocs.com/?ID=10003332_858072

It's like the old line about a purported Japanese invasion of the (lower 48) United States by way of Alaska. "Yeah, they could get here that way, but it would be their grandchildren, who's be speaking English and playing baseball."

[Takao]

Surprised that no one pointed out to AiBosq that the reason the Chunnel was completed in 4 years was because they were working from both ends. His proposal has the Germans working from only one end. Therefore it will take the German far longer tHan 4 years to complete.

Throwing stupid amounts of money and labor at the project will not complete it any faster than the modern Chunnel either, as only a small portion will be dedicated to actually digging and advancing tunnel. Not to mention the lack of modern excavating equipment, and the very finite amount of equipment that can fit in the tunnel.

[maltesefalcon]

I think it actually took six years start to opening day. One of the potential problems touched on in an earlier post was breakdown of military vehicles while inside the tunnel. (Not to mention the wear and tear on the roadway surface by thousands of tracks.)
But the tunnel IRL was never designed for use by motor vehicles. Breakdown issues aside, the air would be rendered unbreathable from the exhaust of so many engines.
The Germans would have to run electric trains as per the original, with enough track at the exit at least to unload. So to render the whole thing useless the RAF just needed to bomb the exit and entrance tracks at regular intervals.

[historygeek2021]

The British wouldn't even need to destroy the tunnel. They could just set up a perimeter big enough to let a few German divisions through at a time, then massacre/capture them one after another. Hitler was so stubborn, he would probably throw away his entire army trying to break through.

[Kingfish]

All this talk of German invasion tunnels and no one has considered the possibility of awakening the Balrog.

[Carl Schwamberger]

Could be a movie. Nazi fanatic think he can control the Balrog with ancient magical Runes & incantations. Of course it ends badly for the bad guys.

[daveshoup2MD]

Could be a movie. Nazi fanatic think he can control the Balrog with ancient magical Runes & incantations. Of course it ends badly for the bad guys.

We need a Downfall version with Bruno Ganz screaming about "dumkopfs delving too deep!"

[Carl Schwamberger]

Im imagining the entries in Brookes diary concerning the Balrog taking charge of Calais.

[Takao]

Meh, feed Goering to the Balrog....it will take 500 years to sleep of that meal.

[LineDoggie]

Lets assume the ORG Todt and Wehrmacht are indeed able to somehow defy odds and build a tunnel into the UK without interference.

It would clearly be a fatal funnel as Known in MOUT/FIBUA where you would site some MG and Artillery and it would direct fire into it causing massive casualties and collapses

the Wehrmacht troops would be severely limited in return fire's due to masking

for Wehrmacht troops caught inside panic would ensue, thousands not hit by enemy fire would die from being crushed in the flight to return to France and safety