The X-51A, an unmanned test aircraft using scramjet technology hit Mach 6 (six times the speed of sound) and stayed there for 200 seconds on May 26, 2010! That is a far cry from what the X-15 managed forty years ago! The X-51 stayed above Mach 6 for an astonishing 200 seconds...Which means it traveled over 220 miles in that time!
for more information, you can go here, here, and here.
This isn't about Washington, but it's darned interesting, so I am sure you won't mind.
That's an Air Force picture, borrowed from cnet.