August 16, 2024: From late April through June this year, a unit of Ukrainian troops surrounded by Russian forces was supplied solely by drones. Food and ammunition were regularly dropped to the Ukrainian soldiers during the 70 day-long battle. Eventually a relief force of Ukrainian troops broke through and enabled the surrounded soldiers to leave the fighting and get some rest.

This is nothing new, in 2009 the U.S. Marine Corps began shopping for a drone to deliver supplies, at least half a ton per trip, in order to get essential items like munitions, water, and food to combat troops in remote locations. The marines wanted the drone available for use within six months, but no one was able to come up with anything in time. In 2010 the marines successfully tested a transport helicopter drone. Some firms told the marines they were working on it, and one of these outfits, Kaman, modified its K-MAX manned helicopter to meet marine requirements. This month, another contender, Boeing, successfully met marine requirements as well, using its smaller A160T.

The first to meet the requirement was the Kaman K-MAX. This 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 marine resupply drone. When tested, it was able to carry a 680 kg sling load to 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 drone can also carry up to four separate sling loads totaling 1,568 kg.

The A160T carried 1.1 tons of cargo to a spot 135 kilometers distant, within six hours. The A160T did this by making two round trips carrying 568 kg sling loads. The A160T was also able to hover at 3,900 meters. The A160T does not have the carrying capacity of the K-MAX but did hold the world record of 18.7 hours of unrefueled flight. The A160T was built mainly for reconnaissance, while the K-MAX is built for hauling stuff.

The A160T is a two ton helicopter, able to fly under remote control or under its own pre-programmed control. It has a top speed of 255 kilometers an hour and was originally designed to operate for up to 40 hours carrying a payload of 136 kg.

The marines were confident enough in the K-MAX drone to pay Kaman $860,000 to fund the conversion of the manned version of a Kaman helicopter to a drone. The marines decided not to buy the K-MAX drone, how many and how soon, or go for the smaller A160T.

Whichever helicopter drone is used, it will use existing flight control software, which allows such aircraft to be moved from its base to its destination with minimal operator effort. Then, once the operator selects a landing area, the flight control software automatically lands the drone. Once unloaded, the operator uses a few mouse clicks to order the drone to take off, return to base and automatically land.

In 2018 the marines tried again, with the AACUS (Autonomous Aerial Cargo/Utility System) that could turn any helicopter into an unmanned aircraft. The marines did not buy any of these, although the system was exported to Jordan, Saudi Arabia and Thailand. AACUS systems sell for $13 million each.

In 2023 the marines ordered 28 TRV-150C TRUAS (Tactical Resupply Unmanned Aircraft Systems) when the system had almost completed development. TRV-150C was ready for use in 2024. Each drone cost $400,000.

TRV-150C is a quadcopter with eight rotors. Each of the four extensions has two rotors, one on top of the other. The drone weighs 68 kg and can deliver that much weight in supplies to troops eight kilometers distant. Carrying no payload, or only 7.5 kg, the drone can deliver to troops 45 kilometers distant. Several TRV-150Cs were sent to Ukraine, where they have performed well in a combat zone. It is unknown if TRV-150C was used for the recent incident where surrounded Ukrainian troops were resupplied by drones during a ten week battle.