كيف كان يتم اكتشاف الطائرات العدوه قبل أكتشاف الرادار ؟

How incoming enemy aircraft were detected before the advent of radar

STRANGE ACOUSTICEARS
BEFORE RADARON A SWIVEL

STRANGE ACOUSTIC “EARS”
BEFORE RADARGERMAN

STRANGE ACOUSTIC “EARS
BEFORE RADARON WHEELS

STRANGE ACOUSTIC “EARS”
BEFORE RADARENGLAND