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

[AiBosq]

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.

[Carl Schwamberger]

& as the first German landser pokes his head out into the Dover countryside, he sees the better part of the British First Army looking back at him.

[KDF33]

& as the first German landser pokes his head out into the Dover countryside, he sees the better part of the British First Army looking back at him.

"And if you gaze long enough into the UK, the UK will gaze back into you."

-Nietzsche, probably

[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.
Given how allied aerial reconnaissance seemed to spot most of the things Germany was building keeping a tunnel producing millions of tons of spoil secret would seem impossible.

[OpanaPointer]

TBMs were massive machines, quite impressive bits of equipment.

[Michael Kenny]

I think the date of the original post is off by a few days.

[historygeek2021]

By 1940 it was extremely easy for European armies to defend narrow points of attack. Armies needed to attack along the entire front, over hundreds of kilometers, in order to find a weak spot to break through. Thus, not even a causeway across the English Channel would have allowed Germany to invade Britain. The entire channel would have been needed to be filled in.

[Carl Schwamberger]

Id expect the Brits would not even bother to counter mine. Maybe drill some holes along the beach & let the incoming tide flood in ?

[john2]

I asked a similar question years ago. viewtopic.php?f=11&t=32826

[OpanaPointer]

Id expect the Brits would not even bother to counter mine. Maybe drill some holes along the beach & let the incoming tide flood in ?

Why not drill past the low tide mark, so there's always water above the bore?

[Carl Schwamberger]

Then you have to bring a drill on a barge. On a truck should be cheaper.

[OpanaPointer]

Then you have to bring a drill on a barge. On a truck should be cheaper.

Dredges routinely sweep areas underwater, adding a drill to the rig wouldn't be a big deal, just make sure you have strong anchors firmly set. A dredge rig might be the perfect camo for this kind of thing.

[Carl Schwamberger]

Dude, you want to run up costs and complicate everything bringing in barges ect... In any case the enemy is going to spot a drill rig of any type at work over their tunnel route.

[OpanaPointer]

How much does it cost to repel an invasion that makes it to shore?

[TheMarcksPlan]

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.

As you seem to realize, there are good reasons the Nazi Chunnel doesn't work: To finish it requires peace-like conditions else it's easy to shoot/drown the finishing stages.

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 once raised a similar question regarding Germany constructing a causeway in the Channel:

I must again emphasize that this causeway idea is not the main or sole point about possible German victory in this ATL. I raised it upthread as an aside, while insisting on more detailed discussion of the '42-'45 timeline before digging into details about the war's end state.

Despite the above caveats, the AHF community did not respond in the open spirit of inquiry in which our questions arise - mostly just with rancorous hostility. The moderators shut down discussion (3, 2, 1...)

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. They thus would turn the threat of crossing between Dungeness and Dover into the threat of a glorified river crossing - far cheaper to mount and harder to preclude than a typical sea landing.

By doing so, Germany would tie down defensive forces in the Dungeness-Dover sector out of all proportion to the defended coastline length, opening up possibilities elsewhere. Or, failing proper British/American response to that threat, they could do the river crossing from the Varnes under massed covering field artillery fire.

Regardless of whether initial landings were glorified river crossings between Dungeness and Dover, a short corridor between the Varnes and Albion could be filled in after the initial battle (assuming it's successful) as a logistical corridor to support a breakout from the initial landings. This is potentially the difference between a landing force being viable only within reach of naval and trans-Channel air forces, versus being able to operate deeply from its beachhead.

-------------------------------

Am I certain that a causeway could work? Not much more than that a Chunnel would work. Do I believe the physics/economics are feasible and worthy of discussion instead of blind hostility? Yes. A Chunnel does exist; the remaining questions are only military/strategic.

I can only recommend not letting AHF hostility deter you from discussion - though we're at the mercy of other powers in letting that discussion take place.