The Blackswift was a proposed aircraft capable of hypersonic flight designed by the Lockheed Martin Skunk Works, Boeing, and ATK.

The USAF states “The Falcon Blackswift flight demonstration vehicle will be powered by a combination turbine engine and ramjet, an all-in-one power plant. The turbine engine accelerates the vehicle to around Mach 3 before the ramjet takes over and boosts the vehicle up to Mach 6.” Dr. Stephen Walker, the Deputy Director of DARPA’s Tactical Technology Office, will be coordinating the project. He told the USAF website,

I will also be communicating to Lockheed Martin and Pratt & Whitney on
how important it is that we get the technical plan in place ...  I'm
trying to build the bridge at the beginning of the program -- to
get the communication path flowing.

The Falcon program has announced the Mach 6 horizontal take-off Blackswift/HTV-3X. It is also launching the HTV-2 off the top of a rocket booster. Falcon seems to be converging from two directions, on the ultimate goal of producing a hypersonic aircraft which can take off and land from a runway in the USA, and be anywhere in the world in an hour or two. Falcon is methodically proceeding toward a Hypersonic Cruise Vehicle. Dr. Walker said,

We need to fly some hypersonic vehicles -- first the expendables,
then the reusables -- in order to prove to decision makers that
this isn't just a dream... We won't overcome the skepticism until
we see some hypersonic vehicles flying.

In October 2008 it was announced that HTV-3X or Blackswift did not receive needed funding in the fiscal year 2009 defense budget and had been canceled. The Hypersonic Cruise Vehicle program will continue with reduced funding.