The promise of hypersonic flight sending us halfway around the world in a matter of hours is being bandied about again, this time by a British company that declares, with all due humility, that it has made “the biggest breakthrough in aerospace propulsion technology since the invention of the jet engine.”

Reaction Engines Limited says its hypersonic engine will send us streaking across the sky at speeds well over Mach 5, allowing us to have bagels for breakfast in New York and sushi for lunch in Tokyo. The hypersonic engine design reportedly includes new ways of cooling the air for an engine that will use oxygen in the atmosphere up to Mach 5.5 before switching to rocket power for the ride in space.

Hypersonic flight has long topped the list of dreamy aerospace ideas. The military loves the idea of super-fast missiles and even bombers, while the rest of us dream of flying from the Big Apple to Tokyo in just a few hours. The big problem has been propulsion. At speeds beyond Mach 2 or so, a jet engine has trouble getting the oxygen needed for combustion. It’s sorta like trying to take a deep breath by sticking your head out the window at 200 mph.