This post is going to be one of those nerdy, thinky ones that isn't really interesting in the least, I'm afraid. Feel free to ignore it, I just needed to get it out of my head, in case I started talking about this stuff in a social setting.
I've been off sick for the last two days, spending my days coughing and trying to avoid watching daytime television. I've been doing a probably unhealthy amount of Wikpedia surfing in order to pass the time and, as there wasn't anything better to do, I have been reading about nerdy things -- technology, inventions, and other general all-purpose "boys' stuff". I spent most of this afternoon indulging my strange fascination with things that got developed, tested, even prepared for full scale production, but weren't ever actually used.
Because of their technical complexity, massive cost, and the public accountability of the people footing the bill, the demise of unwanted military hardware projects are usually the most interesting examples of this, and the ones covered in the most detail by the nerds of wikipedia.
Take, for example, the RAH-66 Commanche. In 1982 the US Army started soliciting proposals for a new armed reconnaissance helicopter, various companies put foward bids and the development of a new aircraft started. It was to have all the bells and whistles you could possibly think of -- sensors and avionics equipment that made it more intelligent than most soldiers, a radar-reflecting body made from composite materials, and an engine that was designed to be much quieter than other helicopters. It made its first flight in the mid-1990s and, after numerous delays, was on track to begin production in about 2004. Unfortunately, by the time the millenium rolled around the US army had learned two things -- 1. unmanned drones are pretty good at reconnaissance and 2. even the most expensive and advanced helicopters can be knocked out of the sky by a nutter with a crusty old soviet-made Rocket launcher. After costing around seven billion dollars of government money, the project was quietly dropped in 2004. It was undoubtedly a cool piece of kit, in a murderous sort of way, but just like the Saunders-Roe Princess, the world moved on before it could be finished.
The strange internal politics and technological one-upmanship of the different branches of the US armed forces means that there's no shortage of projects like this, such as the AH-56 Cheyenne (which was a strange halfway house between a helicopter and a plane, designed to avoid various regulations about what aircraft the army was allowed to operate, that didn't really work as well as either) or, well, pretty much anything in this wikipedia category.
I guess I find this sort of thing interesting because these things were developed by a huge team of engineers, scientists, and designers to fulfill a specific role, and nobody ever really got to find out whether they would have worked or not. Imagine spending years and years working on something only to find that you'll never get to know if any of your cool ideas or late-night moments of inspiration worked.