“Don’t shoot until you see the whites of their eyes,” American revolutionaries supposedly yelled at the Battle of Bunker Hill. Legend has it that the rebels were trying to conserve ammunition, given the inaccuracy of their 18th century guns.

But things have come a long way since 1775. With DARPA’s new “One Shot” sniper system [PDF], scheduled to be in soldier’s hands by the fall of 2011, the U.S. military will give snipers the ability to take out an enemy at a distance of .7 miles in winds around 10 to 20 miles per hour. Military brass hopes the system will give snipers a perfect shot at least six times out of ten.

The One Shot system still wouldn’t come close to matching the record for shooting accuracy: In November of last year, British Army sniper Corporal Craig Harrison made two shots at a distance of 1.53 miles in Helmand Province, Afghanistan. But Harrison modestly thanked perfect shooting conditions: no wind, great visibility, and mild weather. The DARPA program aims to give soldiers the technology to hit a target despite adverse conditions.

To meet that goal, engineers first had to figure out what to do about wind. The prototype gun can’t get rid of the wind, but it needs to correct for it. Otherwise, over long distances, the bullets will veer off course; DARPA notes that a 10 mph crosswind can produce a miss even at a distance of a quarter of a mile.

The One Shot sniper scope has a computer system that uses lasers to track not only distance, but also the wind turbulence in the path of the bullet. A set of crosshairs appears not in direct line with the gun’s barrel, but instead where the bullet will actually hit, and also displays the confidence of that shot.

US military trials have found that a laser beam shone on the target can do more than just determine the range: it can also be used to “measure the average down range crosswind profile”. The laser information can be combined with automatic readings of temperature, humidity etc and a “ballistic solution” computed. [The Register]

But there’s more work to be done on the One Shot system before it arrives in combat zones. These high-tech systems can’t require a lot of training or give off a lot of heat.

What the agency really wants is a battle-ready system that doesn’t require tricky in-field optical alignment and fiddling with lasers. Night and day accuracy also means that the laser, which is used to help calculate and subtract wind turbulence between the predator and his prey, can’t be infrared. Enemies with night-vision goggles would see that from a mile away. [Wired]

DARPA has just finished its first phases of the project, developing and testing the computer targeting system. Among other things, the next steps include making the system the right size and weight for battle, and completing some tweaks to the target crosshairs. With these improvements, according to a DARPA announcement this month, the Agency will ask for 15 “fully operational and field hardened systems” for field testing.

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Image: flickr / The U.S. Army