A couple of US Air Force F-15 Interceptor jets were patrolling the skies above New York City for a period of time after the second passenger plane hit South Tower of WTC.  The elongated objects underneath the wings are not missiles. They are external fuel tanks allowing these jets to extend their effective flying range.

This photo montage is of low quality because it consists of two highly cropped original photos taken handheld at ISO400 and lens set at effective 480mm optical zoom.