The ST-35 Hrim, marketed in English as Silent Thunder, is a Ukrainian loitering munition system from Athlon Avia. Official materials describe a 9.5 kg expendable air vehicle launched vertically by a multirotor that then acts as a relay, while later Ukrainian and exhibition reporting place the system in demonstrated, final-development, and display contexts rather than documented battlefield service.
Athlon Avia describes ST-35 Hrim as a backpack-portable loitering-munition package rather than a conventional runway-launched UAV. A multirotor raises the munition for vertical release, then can return for a relay-module fit so the operator can maintain control and receive payload data while the munition flies toward the target area.
Vertical launch by multirotor from a concealed position.
Three expendable munitions, ground control equipment, optical payloads, warheads, a multirotor, relay hardware, antennas, and support equipment.
Automatic attack mode using television or infrared channel guidance after operator target detection and confirmation.
Hrim is the Ukrainian-language name used with the ST-35 designation; Athlon Avia markets the same loitering-munition system in English as Silent Thunder.
| Variant | Configuration | Designation notes |
|---|---|---|
| ST-35 Silent Thunder | English marketing designation | Athlon Avia's English product page uses ST-35 Silent Thunder for the loitering munition system, while Ukrainian sources use ST-35 Hrim. Sources: ST-35 Silent Thunder | Athlon Avia - Unmanned solutions, Presentation of the ST-35 Hrim unmanned aerial system |
Published ST-35 materials describe several swappable payload types for the loitering munition.
| Carried item | Item type | Carriage evidence |
|---|---|---|
 | Fuel-air explosive payload type | Athlon Avia and Defense Express list a fuel-air explosive or thermobaric warhead option for the ST-35 Hrim/Silent Thunder loitering munition. Sources: ST-35 Silent Thunder | Athlon Avia - Unmanned solutions, ST-35 Hrim combat-warhead tests planned for summer 2022 |
Ukrainska Pravda reported that Ukraine unveiled the ST-35 Hrim drone in 2019 as an Athlon Avia loitering munition with an X-wing configuration.
Sources: A scalpel against air defences: no more asking Where's Ukraine's Lancet?
Ukrainian Military Pages reported that Athlon Avia released a video presentation for the ST-35 Hrim, covering its system composition, portable and mobile versions, and combat capabilities.
Sources: Presentation of the ST-35 Hrim unmanned aerial system
Defense Express reported that combat-warhead tests were planned for summer 2022 and described the system as still under development.
Sources: ST-35 Hrim combat-warhead tests planned for summer 2022
Defense Express reported Athlon Avia's statement that the Silent Thunder project was in a final phase, while giving no direct fielding or combat-use claim.
Sources: Ukrainian company nears completion of Silent Thunder system
Army Recognition reported that Athlon Avia displayed the ST-35 Silent Thunder loitering munition at UMEX 2026 in the United Arab Emirates.
Sources: Army Recognition UMEX 2026 ST-35 display
Ukrainska Pravda contrasted Hrim with later Ukrainian mid-range loitering munitions and reported that Hrim did not make it to the battlefield.
Sources: A scalpel against air defences: no more asking Where's Ukraine's Lancet?
