Cub Driver wrote:

For security reasons, subterranean runways/airports were proposed
during WW-II. Perhaps the time has come to consider that proposal
again.

Switzerland in the 1970s (and probably before and since) had
underground hangars built into the mountainside. However, the planes
taxied out of them and onto the highway, which became the runway.

I dunno about that. There isn't a straight stretch of road or highway
in all the mountainous areas of Switzerland, it seems to me. And I've
been on 'em, on those Postal Bus routes. It'd be a mighty short-field
technique taking off from one of those roads!

They do have air bases in CH which have regular-old runways.

Rob