What anti-aircraft defense?

Anti-aircraft defense is the way in which people and places are protected against attack by enemy airplanes. The main purpose of anti-aircraft defense is to knock enemy bombing planes out of the sky. This can be done in either one of two ways. The first way is to have a strong air force that can battle the enemy planes in the sky and keep them from reaching their targets. The second way is to have many guns that fire from the ground at the enemy planes.

Airplanes were first used in battle in World War I. Anti-aircraft defense began at the same time. The airplanes used in World War I did not fly very fast or very high. Soldiers on the ground fired machine guns at the low-flying enemy planes. They were sometimes able to knock a plane down. Airplanes developed rapidly after World War I. On the ground, anti-aircraft guns developed as rapidly as airplanes. Today's anti-aircraft guns automatically fire large shells high into the air.