noun-modifying (irregular), noun which may take the genitive case particle 'no', noun
anti-aircraft
Used attributively for weapons, defenses, or operations against aircraft. Common in military and technical contexts.
The anti-aircraft missile intercepted the enemy plane.
Anti-aircraft guns are deployed at the base.
対空 describes weapons or actions directed against aircraft, whereas 対地 describes those directed against ground targets.
対地 describes something aimed at or relative to the ground, while 対空 describes something aimed at aircraft, so the two are easily mixed up despite the identical 対〜 pattern.
Compound of 対 (たい, 'against') and 空 (くう, 'sky'). The exact historical derivation is uncertain, but the spelling is conventionally associated with anti-aircraft meaning.