An inept North Korean pilot in an obsolete plane attempts (and fails) to bomb the ammunition dump placed near the 4077th every day at exactly 5 O’clock by dropping a grenade from his plane. Major Burns decides a serious reaction is in order, so he requisitions an anti-aircraft gun and attempts to shoot the plane out of the sky, with predictable results.

This was loosely based on experineces of US Marines In World War II. The plane is a Ryan PT-22MASH Wikipedia