The Defense Advanced Research Projects Agency (DARPA) is developing a system that will assist helicopter crews in pinpointing the source of small arms fire.
In testimony before the Subcommittee on Terrorism, Unconventional Threats and Capabilities of the House Armed Services Committee, DARPA director Dr. Regina E. Dugan announced the (or HALTT) program. Continuing the military tradition of silly acronyms for deadly systems, HALTT uses advanced acoustic detection and data processing to “exploit the supersonic shock wave produced by a bullet in flight.” In other words, it would detect the “snap,” “hiss,” or “crack” of a bullet.
Or if you remember the following from Black Hawk Down:
Grimes: Why aren't you shooting?
Waddell: We're not being shot at yet!
Grimes: How can you tell?
Waddell: A hiss means it's close.
After detection, HALTT would alert the crew and provide shooter location with “o’clock accuracy” (i.e. “Hostiles at 12 o’clock!”). Enemies would have to think twice before engaging US forces, because with HALTT, "the first shot may very well be the adversary’s last." And according to Dugan, small arms fire accounts for 85% of hostile fire engagements, so HALTT would be tremendously beneficial.
A prototype HALTT system has already been installed and tested on a UH-60 L Blackhawk. The next step is “operational evaluation” (i.e. field testing) in Afghanistan, and the finished product should be fielded within a year from “identification of need.”