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I would argue that the civil engineering technology was not yet at a level to build a 32 mile long tunnel under the English Channel.From the early 19th century there were proposals to build a cross channel tunnel from England to France.
In the 1880s a tunnel was actually started, with excavation from both the French and English sides, but this was abandoned due to the British military fearing it would aid a cross channel invasion.
After WW1, in the interwar period, there were a few proposals for a cross channel tunnel, one of the proponents of the tunnel being Winston Churchill.
After France fell there were fears in Britain that the Germans could build a tunnel, or two, in 18 months.
My question is - if the tunnel from the 1880s was completed, or one of the proposals from the 1920s was built, how would that effect the war?
Would it increase the chances of a successful invasion of Britain by Germany?
Or would such a tunnel be too easily defendable?
Agreed. Certainly not in the 18 month timescale claimed.I would argue that the civil engineering technology was not yet at a level to build a 32 mile long tunnel under the English Channel.
The Simplon Tunnel in the Alps opened in 1906 and is 12.5 miles long. There were other long mountain tunnels, but for underwater tunnels the lengths were two miles and under, such as the Holland Tunnel and the Lincoln Tunnel.Agreed. Certainly not in the 18 month timescale claimed.
After 20 years of site investigation and planning a route across construction work started in 1988. Working from both ends from 1988 with late 20th century automated tunnel boring machines both cutting the tunnel and lining it with pre-cast concrete panels it took until 1 Dec 1990 to achieve a breakthrough in the first (narrower service tunnel). The route chosen was not simple to achieve due to the geology.
I'm sure the British Army would have welcomed narrow columns of emerging German troops with the open gates of a POW cage. Plenty of time to plan for that.
Edit:- Just for comparison it took the Japanese 6 years 1936-42 to construct the twin tunnels of the Kanmon Rail Tunnel between Kyushu & Honshu islands. Don't know about the geology, but they were only 3.6km long.
Edit 2. Each end of the 1880 tunnel had only progressed about a mile in 9 months before the project was abandoned. Slave labour doesn't really help much due to the narrow working face at the front of the tunnel.
And if you had Australians in the mix it would have ended even quicker due to their going elsewhere to look for decent coffee…There would have been a Starbucks on the French side of the tunnel to serve hot coffee to the GI's. With the GI's full of caffeine the war would have ended six-nine months sooner.
But they were not large enough to carry trains or vehicles.FWIW
There is/was the Rothschönberger Stolln dewatering adit, part of the "Revierwasserlaufanstalt Freiberg - Wikipedia", mostly built between 1844 and 1877, at a little over 31 miles long by 10-20 ft wide. It was the longest tunnel in the world until the Delaware Aqueduct, built between 1939 and 1945 to feed water to New York city and metro area, at a little over 85 miles long with a diameter of 13.5 ft.
On the other hand it was common knowledge that the Maginot line was unbreakable and Troy wouldnt fall and that strange RN ship against the the heavily dry dock at St Nazaire would not be a problem.To be honest, I don't think that a Commander would risk his army in such a precarious situation.
All the British would have to do, is wait until the invaders reached the English side and detonate the mines, resulting in a total annihilation of countless troops.
Much like in the Biblical story of Moses releasing the part in the Red Sea upon safely reaching the east side, which engulfed Pharoh's charioteers and troops who were in hot pursuit.
The solution to any tunnel being denied enemy access, is not to blow up the whole tunnel. That would be wasteful because they would eventually have to rebuild the tunnel.To be fair, the under-channel tunnel idea would only work if it could be built in secret - which secret would be impossible to keep due to the time involved, if for no other reason.
I would think that capturing the enemy end intact would be the ultimate commando operation. You wouldn't even think about marching your own troops through unless both ends were secure, and the middle likely safe from any naval operation.
Considering the Wehrmacht's fateful pause while the BEF and French were crowded unmolested on the beach, I'd suspect their escape via the tunnel would have been successful.So a tunnel would have been great for evacuating after the fall of France, so long as you can hold the tunnel entrance and you can get your troops to the tunnel.