[schlowmo]

What the english version of this wikipedia article doesn't mention (the german version does) is that the usage of this tunnel shifted a lot in recent years.

Today it's a very important bike route for people living south of the river Elbe (especially in the districts Wilhelmsburg and Veddel, both experienced heavy gentrification in the last two decades).

While the english version only states yearly usage numbers for 2008 (300k cars, 63k bikes, 700k pedestrians) the german also has numbers for 2018 (52k cars, 300k bikes, > 1 million pedestrians).

In my own experience the pedestrians are mostly tourists and the cars people working at the shipyards south of the river Elbe.

I witnessed a lot of conflicts between pedestrians for which crossing the tunnel is some kind of special experience getting in the way of cyclist which just want to get from one side of the river to the other as quickly as possible. There are sidewalks on both sides of each tube but tourists don't care much.

But I guess this is kind of inevitable if such a curiosity is part of the daily used traffic infrastructure.

[ncmncm]

Wondering if it was used for wartime production, for protection from bombings.

German aircraft production increased each month right up until substantial homeland territory was lost, apparently unaffected by massive bombing. Given its military futility, most of the bombing should probably be considered war crime. Air crews' lives were squandered.

[LargoLasskhyfv]

Unlikely. Parts of it are above the river bed, and stick out into the water. It's all rather fragile patchwork, not some massive reinforced concrete thing.

This sticking out is also the reason all the terminals for larger ships are downstream of it, because their keels would crunch it, even at high tide.

[nielsole]

When I was constructed, the tunnel did have 3m of sediment on top of it. This was required, as the tunnel was dug horizontally. Unless that changed over time, no part of the tunnel should be exposed.

[LargoLasskhyfv]

I do know that. But I think the graphics in Wikipedia visualizing the profile are wrong. I've been into exhibitions about it, which showed much more than that. Also it may have been different at different times because the river is dynamic, has been and is been dredged out, from time to time, as necessary.

The roof of the tunnel is too high in the water, to let contemporary large ships pass. Where large ships means the giant container freighters with 19.000+ TEU capacity. Mission impossible. Covered or not. This is not true for roll on/roll off ferries, or some cruise ships which seem similarily large, but aren't, at least not below the waterline. They just manage, but barely.

It is a barrier inhibiting ships with large draft/draught from passing. Which is why all the terminals servicing them are downstream.

[derda]

I dont know about the use as a shelter, but you might be interested in the fact that one of the largest german shipyards Blohm & Voss is right at the south side of the tunnel.

[1] - https://en.wikipedia.org/wiki/Blohm%2BVoss