US Navy Railgun Program
So, I just found out about this today, but apparently it's been out in the open since spring. The US Navy has been designing a functioning railgun that's been tested in laboratory conditions and shown to be capable of hurling a projectile at Mach 7 speeds through several walls of reinforced concrete and multiple steel plates.
The price of each projectile is $25,000 at the moment, and this is likely to become cheaper as production methods mature. At that price, it's cheaper than the missiles it will be used to destroy.
Now, I know what you're probably thinking--but won't the gun be expensive? Yeah, it seems like it would be, especially considering it relies on an electromagnetic phenomenon called the Lorenz force, but according to the Navy's budget, between 2005 and 2011, the entire program ran up a bill of $250 million. An exorbitant amount of money in civilian terms, but as US Military budgets go, that's dirt cheap--that's less money than the airforce spends building two F-22 Raptors. Even better, the program is projected to only spend another $250 million by 2017, and by that time it's expected to start sea-trials.
I was happy to see this news and I hope that it's a success because I'm tired of seeing the US Military spending billions on researching new technologies only to determine after going way overbudget that the technology either isn't feasible, economical, or doesn't actually confer any advantage over our current capabilities that would be worth the cost.
Also...we're like... ermm maybe twenty years from mounting these on whatever vehicle replaces the Humvee and creating Gausshogs.
http://www.wired.com/2014/04/electromagnetic-railgun-launcher/
http://www.cbsnews.com/videos/us-navy-unveils-high-speed-rail-gun/