Most people have experienced the sonic boom of a skillfully wielded whip, or the closely related crack of a nearby bolt of lightning. Such sounds have a character that attracts a good deal of attention, which is why the US Special Operations Command (SOCOM) is trying to silence them. The crack of a rifle shot is the sonic boom of a supersonic bullet, making stealthy ground missions difficult to accomplish. To address this need, SOCOM has issued a Small Business Innovation Research request for proposal (SBIR-RFP) for a feasibility study of suitable subsonic rounds.
Read the full article: US Special Forces seeking subsonic ammunition for covert missions