Flying killer robots are numerous these days. The machine flyboys are mostly armed with relatively light and precise weapons, but still in the tank- or anyway vehicle-busting league. Now, however, there's a droid whirlybird in development which is armed only with a sniper rifle intended to fire single aimed shots.

The new issue of Popular Mechanics reports on the robosnipercopter, dubbed the Autonomous Rotorcraft Sniper System (ARSS) in a fit of American insularity. (This is not unusual.) The magazine says that the ARSS programme, underway since 2005 within the US Army's Aviation Applied Technology Directorate, is to enter flight tests this summer.

The goal of ARSS, as stated by the Army, is to produce a system "having the ability to accurately engage single point man sized targets with an airborne UAV ... [giving] the ground based soldier the ability to have a high-point survivable sniper at their disposal when needed. An airborne UAV can rapidly achieve lookdown angles and viewpoints required for sniper engagements, while controlled from the troop on the ground."

The Army boffins already had a Vigilante robocopter on hand as a result of their Armed VTOL UAV Testbed Integration (AVUTI) effort. This produced a Vigilante (essentially an automated Ultrasport 496 kit chopper) remotely controlled from a station which can be set up on the ground or strapped into a manned transport helicopter for better radio line-of-sight. US Apache attack ships can now be fitted to control unmanned aircraft, too.

The original AVUTI Vigilante was armed with 70mm rocket pods and a laser designator: weapons on the same sort of level as the Hellfire missiles used in the famous Predator and Reaper roboplanes, or the Fire Scout droidcopter. They are fairly light in air-weapons terms, but still cause a big bang when they hit. That's fine for a lot of traditional military jobs like taking out a strongpoint or an enemy vehicle.

But in modern warfare, especially urban warfare, you often need to use a lighter touch. Hellfires, Hydra rockets, "Viper Strike" miniglider smartbombs and so on cause collateral damage - deaths, injuries and destruction - which may wipe out any gains achieved by killing the target. For this reason, military snipers have made a huge comeback in recent years: their long-ranging accurate rifles (and advanced sneaking skills) let them clear away hostile snipers, machine gunners, ambushers and so on without hurting anyone else or smashing the place up. Snipers are also a preferred option for stopping enemy vehicles: a high-powered bullet into the engine does the job just fine, and lets you interrogate the occupants afterwards.

Traditionally, military snipers have tended to move about on foot, using concealment and camouflage to evade the attention of surrounding enemies. In urban fighting, they often work from rooftops or other high points in "overwatch" over the largest possible area. This does have the downside that they take a long time to get into position.