WHOOSH!

Modes of transportation tend to go through periods of rapid improvement followed by long periods of roughly steady performance.  Railroads were invented in the 1830s, and by the 1870s trains hit speeds of more than 60 miles per hour -- which is where train speeds remained for nearly a century.  Then, in the 1960s and 1970s the Japanese Shinkansen and French TGV trains kicked up the speeds to more than 100 miles per hour.

Similarly, within two generations after the Wright Brothers, propellor planes had maxed out at about 500 miles per hour.  That's where things remained until jets pushed the limit up to the speed of sound.  Once the "sound barrier" was broken, jet speeds increased rapidly . . . until they stopped.  The fastest plane in the world is the SR-71 spy plane, which set the record of Mach 3.3 on its retirement  flight.  The plane first flew in 1966, which means no faster plane has been built during the lifetime of a middle-aged game designer.

That may change soon.  Researchers at Pratt & Whitney are testing hypersonic engines capable of shoving a plane up to Mach 6 -- or possibly as fast as Mach 15!  This Popular Science article discusses the matter in more depth. 

Having recently flown to Tokyo on a subsonic jetliner, I think the idea of making the voyage in two hours or less has a great deal to recommend it.  And if you're tooling along at Mach 15 anyway, you're almost halfway to orbital velocity, which means a hypersonic scramjet plane is a big step toward a true "spaceplane."  So NASA likes the idea.  Naturally the Air Force likes anything which makes planes and missiles go faster, and of course the deranged geniuses at DARPA are involved because hypersonic ramjets are just totally wicked.