The RQ-8 UAV recently demonstrated a new feature that enables it to deliver two cargo containers. Unfortunately, the max payload of the RQ-8 is 272 kg (600 pounds). That's because the RQ-8 is based on a two seat civilian helicopter (the Schweizer Model 333), which has a maximum takeoff weight of 1.5 tons. With its rotors folded (for storage on ships), the RQ-8 is 23 feet long and 9.4 feet high. The flight control software enables the RQ-8 to land and take off automatically. Each RQ-8 UAV costs about $8 million (including a share of the ground control equipment and some spares.) It was developed for reconnaissance, not supply runs.
The U.S. Marine Corps recently successfully tested a transport helicopter UAV more capable of moving serious amounts of cargo. The K-MAX is a 5.4 ton helicopter with a cruising speed of 148 kilometers an hour and an endurance of over six hours. It can carry up to 2.7 tons slung underneath. This made the K-MAX an ideal candidate for the cargo UAV the marines were looking for. K-MAX was able to carry a 680 kg (1,500 pound) sling load to 12,000 feet (3,900 meters), and hover. It was able to deliver 2.7 tons of cargo, to a point 270 kilometers distant, within six hours (two round trips). The K-MAX UAV can also carry up to four separate sling loads (totaling 1,568 kg, or 3,450 pounds).
The RQ-8 has been in development for years, but the U.S. Army lost interest. The U.S. Navy will still use the RQ-8 on warships, mainly because it can operate from a ship. Land forces are not as interested in helicopter UAVs, except perhaps for very small ones, what can hover in urban areas and transmit video. The marines are intent on using a larger helicopter UAV for delivering critical supplies to troops. The U.S. Army Special Forces has also expressed interest in this sort of thing, and it may have been the Special Forces that the RQ-8 mod was directed at.