"Combust" by GrimGrum (https://freesound.org/people/GrimGrum/sounds/412558/). Licensed under CC0 1.0 (https://creativecommons.org/publicdomain/zero/1.0/)
"Military Helicopter" by Benboncan (https://freesound.org/people/Benboncan/sounds/74242/). Licensed under CC BY 3.0 (https://creativecommons.org/licenses/by/3.0/)