Dr. J. Allen Hynek:
One year prior to the radar-visual UFO sighting by the aircraft carrier Philippine Sea, the ship was involved in a double radar UFO sighting with the carrier USS Princeton off the east coast of Korea.  The Princeton had made radar contact with several high-speed “Unknown” during April and May of 1951 prior to the double contact involving radar aboard the Philippine Sea. The speeds of the “Unknowns” were estimated at up to 1,200 MPH.  Excerpts from a letter to the Chief of Naval Operations from Commander Naval Forces, Far East, dated September 11, 1951, and classified SECRET,  contained this report: 

The observation of rapidly moving targets on the PPI scope of the SX radar on the USS Princeton, CV-37,  has been reported by Lt. H.W. White, a CIC watch officer on the staff of Commander, Carrier Division 5.  The targets were observed several times while operating with Task Force 77 during April and May of 1951. On one occasion the targets were observed by two ships simultaneously. The same targets were held by both the USS Princeton and USS Philippine Sea on their SX radars.  The ships were approximately 4 000 yards apart at the time.  The tracks made by the contact on the radar of the Philippine Sea were the same as those on the USS Princeton. The targets were always 22° wide and sharply defined.  The presentation was exceedingly bright in comparison with normal air and surface contacts.  Appearance of the target never varied.  The SC radar wad operating satisfactorily both before and after each incident. Very little sea return was observed. Although previous observations of high-velocity targets had been reported by aircraft, this report was the first reported shipboard occurrence of this phenomena.  This report is considered of particular interest in that the contacts were observed by two different radars at the same time, thereby reducing the probability that malfunctioning ofthe radar was the cause of the phenomena.