Somewhere between the Wright brothers and the walk on the moon, there were the planes designated "X," 1 through 15.

There was also a group of daring young men on an assortment of dangerous flying machines who broke the sound barrier and then some. (And, at a painfully wasteful rate, broke their planes and often themselves in the process.)

NBC, with some astonishing footage never before shown, traces the development of the X-1 through 15 in a 90-minute news special, "An American Adventure -- The Rocket Pilots," shown on Channel 4 at 9:30 tonight.

Although the '30s and '40s air adventures of Clark Gable and other cinematic test pilots pale in comparison with those of the pilots of the X planes, and although the space shuttle Columbia is more a child of the X than of the astronaut-manned missiles, the X pilots are virtually anonymous. Obsolete in their own time, you might say.

NBC has found several of them, however, for its documentary. One is retired Air Force Gen. Charles Yeager. Remember him? Sure you do. He broke the sound barrier in 1947.

And then there's scientist-pilot Scott Crossfield who hit Mach 2, twice the speed of sound, and helped design and was the first to fly the X-15. Crossfield walked away from a crash of an early model X-15 in which the plane broke in two. When you consider that the fuel was a mixture of liquid oxygen and alcohol, the chutzpah of these pilots must be admired, if that's the sort of thing you admire.

Much of the work the X pilots did was Cold War-related and classified top secret, so they never got the ticker-tape parades and White House receptions, as the program's narrator Lloyd Dobyns points out. Their mission was to erase the humiliation America suffered at the launch of the Russian Sputnik, but that was not to be until Cape Canaveral, John Glenn (and friends) and Capt. James T. Kirk of the Starship Enterprise began to get their respective acts together.

It really wasn't fair, especially after Col. William "Pete" Knight, in the X-15, became the fastest man alive at a cool 4,520 miles an hour.

He is still head of flight testing at Edwards Air Force Base in California, and his speed record stood for 13 years, until last spring's flight of the Columbia.

The NBC documentary makes a greater contribution to history than to popular TV, especially when you look at its tough competition tonight. But it was an exciting and dangerous time that deserves its chronicle, and we wouldn't be where we are, spacewise (budget cuts notwithstanding), but for these foolhardy adventurers.