Inspired by this thread, what wacky engineering/construction proposals have died a merciful death: Smog tunnels? - Factual Questions - Straight Dope Message Board
I can recall two, off the top of my head, and both were concocted during warfare. First is the WWII iceberg aircraft carrier: Project Habakkuk - Wikipedia
and number two is CIA “Project Able”, to use satellite mirrors to illuminate much of South Vietnam and deprive the enemy of the cover of darkness to conduct operations.
Here’s a link that mentions Project Able: http://jcgi.pathfinder.com/time/magazine/article/0,9171,843267,00.html
I don’t want to beat a dead horse here, but I can’t believe that no one else can think of some colossal project that was misconcieved. I’ve thought of another example, although I don’t know if it ever got past the talking stage. It was a few years ago when there was a proposal to pipe water from the Columbia river to southern California.
There must be some other examples. Anybody?
I don’t think there’s anything wrong with that concept, and it certainly didn’t end there. The Russians actually tested this idea in space.
I hadn’t heard of that one, but you have to remember that Project Able was proposed over 30 year before and I doubt that much thought was given to the environmental impact. Of course the cost, in the late sixties, would have been extreme, to put it mildly.
One of my faves was a nuclear power plant being built. It was a huge building and there was another that was a mirror image. In engineering you order shown and opposites . The procurer order 2 of everything. It is the Guiness biggest financial error ever.
There was the idea for a nuclear powered aircraft. Ford wanted to build a car called the Nucleon which was also nuclear powered.
My Dad swears up and down that the Army Corp of Engineers once seriously proposed to flood the Grand Canyon to use as a source of electricity in the west, and that doing so was seriously considered.
::off to Google::
The prototype was turned over to George Barris, who customized it for an unidentified billionaire. 
On a more serious note, in the 1950’s, the Rover Corp. was trying to perfect a jet-turbine powered car.
Chrysler had a prototype turbine-engine car, too. Problem with turbine engines in a car is that you let off on the gas and the engine doesn’t lose RPMs right away as a piston (or, for that matter, a rotary) engine would.
