Flying drones are a risky way to rescue wounded troops. A Ukrainian official says they're a 'lifeline of last resort.'

Ukraine has begun using heavy-lift drones for casualty evacuation missions.

Stringer/REUTERS Ukrainian forces said Monday that they pulled off a "first-ever" air evacuation using a heavy drone.

Deploying large aerial drones for battlefield casualty evacuation is a high-risk operation.

A Ukrainian official involved in the development of such drones called them a last-resort tool.

Several Ukrainian companies have developed heavy-lift drones that can evacuate wounded soldiers from the battlefield, but the risks mean they should be used only as a last resort, an official involved in these efforts told Business Insider.

Denys Lohvynenko, the drone chief at Brave1, Ukraine's state-backed innovation platform , said that heavy-lift drones provide a time-sensitive means of rescuing wounded troops in highly dangerous situations where they cannot walk on their own and other evacuation methods are unavailable.

Ukraine began developing heavy-lift drones two years ago, but the complex technical requirements took time to iron out.

On Monday, a Ukrainian military unit said that it had used a heavy drone to save a wounded soldier from the front lines, carrying out what it described as a "first-ever air evacuation." The presence of land mines and Russian drones rendered the use of ground robots — for Kyiv, an increasingly common method of casualty evacuation — too challenging.

"In these situations, heavy-lift aerial evacuation serves as a lifeline of last resort," Lohvynenko explained in remarks shared by Brave1, which has supported the development of these drones and other war technology.

Ukraine's 92nd Separate Assault Brigade said Monday that soldiers used a six-rotor hexacopter made by the Ukrainian company Gurzuf Defense to carry out the mission.

Other defense companies are working on similar technology; SkyFall , for instance, recently unveiled its own hexacopter for evacuations.

Ukrainian forces also use heavy-lift drones for logistics missions , as they can typically carry more cargo than smaller variants.

A challenge is that big drones are big targets.

Samuel Bendett, a drone warfare expert at the Center for Naval Analyses, a US research organization, told Business Insider on Monday that certain elite Russian military units are focused on downing such aircraft.