AIRFIELD DEFENCE SITE

SN A site or building associated with active or passive defence of the landing ground and buildings of an airfield.
CL MILITARY DEFENCE AND FORTIFICATION
BT DEFENCE SITE
NT ANTI LANDING OBSTACLE
BATTLE HEADQUARTERS
BISON MOBILE PILLBOX
PICKETT HAMILTON FORT
PILLBOX (AIR MINISTRY PATTERN)
SEAGULL TRENCH