From the Document: "A new generation of supersonic (faster than the speed of sound in level flight, also called Mach 1) passenger aircraft is now under development. Using 'low-boom' technology developed through NASA research to minimize sound signatures on the ground, advanced engines, and alternative fuel concepts, these new supersonic transports (SSTs) advertise the ability to fly over populated areas with minimal disruption, cruise more economically, and avoid some of the potential negative environmental effects of carbon-based fuels in high-altitude flight. These new aircraft have attracted interest and some investment from the U.S. military, and have on occasion been proposed for military missions by their developers. The potential roles differ with the size and capabilities of each aircraft."
CRS In Focus, IF11778
Congressional Research Service: https://crsreports.congress.gov/