The DARPA was, and is the Defense Advanced Research Projects Agency, and it exists as 'the central research and development organization for the Department of Defense (DoD)'- a statement that comes from the DARPA homepage.

Way back in the 1960s, one of the projects that they were working on was a little thing known as the DARPA Network, or DarpaNet. This was a system whereby all the missile silos, mountains, American DoD, British MoD¹, and suspicious-looking bunkers were linked up by a whole network of wires, the idea being that if the links from one place to another were severed, for one reason or another, an alternate route could be taken and with the number of wires that there were there would be a near infinite number of possible routes.

This system worked so well that when DARPA finished with it, and moved onto something else (called MilNet) it got opened up to universities, so that they could share information. After another while, ISPs² such as Compuserve started using it, and it developed into what we now have, the Internet.