Foo Fighters (WWII, 1944-45).
documentedmass_sighting_waveScandinavian "ghost rockets"
Glowing balls/lights reported by Allied night-fighter and bomber crews over Europe and the Pacific that paced aircraft, matched maneuvers, and vanished; never attacked, never recovered.
Well-attested pre-1947 military-witnessed aerial-anomaly reports (esp. the US 415th Night Fighter Squadron). Reports are documented; the cause was never established - leading candidates are atmospheric/electro-optical phenomena plus night-combat misperception. A genuine unresolved residue.