A downed US F-15 pilot's account suggests Iran's cheap drones are far more advanced than US and Israeli intelligence realized — bad news for both militaries.

• The pilot, shot down over Iran in April, described swarms of linked drones moving as one, shaped like a jellyfish, with smaller drones hanging below larger ones.
• US intelligence is split: some call it alarming proof of advanced tech, others doubt the account because the pilot was concussed and had been shot down twice.
• The bigger lesson is cost: Iran floods the sky with $200 drones, forcing the US and Israel to burn expensive, hard-to-make interceptors to stop them.
• The same cheap-drone tactic is showing up in Ukraine and with Hezbollah in Lebanon, leveling the field against bigger militaries.

Outlook: Cheap drone swarms look set to keep eroding the advantage of costly fighter jets and missile defenses, making big powers more wary of invading.