McAir report No. E-578, dated May 24 1966 explaining the characteristics of the US Air Force F-4D aircraft. Also, the differences from the F-4C. Credit: Greater St. Louis Air and Space Museum
The report states: “ The F-4D is the second fighter version of the Phantom II family to go into service with the USAF. The F-4D has essentially the same airframe and engines as the F-4C. Major system improvements have been made which increase the aircraft's air-to-air gunnery capability and air-to-ground conventional weapon delivery accuracy. These improvements consist of the addition of a Lead Computing Optical Sight (Drift Stabilized), a Weapon Release Computer Set and a modification to the Inertial Navigation System to provide the necessary inputs to the Weapon Release Computer and the Lead Computing Optical Sight. In addition, the F-4C air intercept radar (APQ-100) has been modified for the F-4D (APQ-109) to provide air-to ground
range input to the Weapon Release Computer. To house the additional electronic equipment, a new equipment bay has been added above the #1 fuel cell. The following pages briefly describe the F-4D and use of the new systems.”