EARLY WARNING SITE

SN A site, building or structure used for the detection of approaching hostile aircraft, shipping or missiles early enough to allow a counterattack or defensive measures to be taken. Use more specific term.
CL MILITARY DEFENCE AND FORTIFICATION
BT DEFENCE SITE
NT ANTENNA ARRAY
EARLY WARNING STATION
ROYAL OBSERVER CORPS SITE
SONAR STATION
SOUND MIRROR
SOUND MIRROR BUILDING