system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do big military aircraft like the C130 and the A440 use propellors instead of jet engines like commercial aircraft?

Am I even asking the right question? It just seems...weird to me. Makes them look ancient even though the A440 launched just two years ago!
gpt
Propellers are more fuel efficient at low altitudes where the air is thicker. Low-altitude aircraft use propellers, high altitude craft use jets.

Combat planes need to be able to go high altitude, so they're all jets. But you can more more stuff more cheaply if you use propellers for cargo.