Most bullets make small sonic booms when flying through the air, which to our ears sound like a loud, distinct "crack!" For the Pentagon's special forces, that makes it hard to be sneaky about what they're shooting. Now the commandos want to be sneakier with slower, quieter bullets.
In its latest round of small-business solicitations, the Pentagon's Special Operations Command, or SOCOM, is seeking out subsonic ammunition. The reason, according to the solicitation, is to "provide superior covert and stealth capabilities" for not only the military, but police forces and the Department of Homeland Security. In theory, and for rifles in the 5.56, 7.62 and .338 calibers, the bullets will travel at low enough velocities to avoid breaking the sound barrier, thus creating no "crack" noise. Breaking the sound barrier also pretty much negates the use of a sound suppressor, or "silencer," which the special forces would likely want to use against militants in Afghanistan and around the world.