AiBosq wrote: ↑
06 Apr 2021 23:36
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:
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."