Why do you think Robert McNamara recalled the fighter plains that were on their way to defend the Liberty?

Answer 1

He was afraid of offending the jews.

Answer 2

"U.S. rescue attempts"

"At least two rescue attempts were launched from U.S. aircraft carriers nearby but were recalled, according to David Lewis, officer of the deck (OOD) during the attack. Lewis wrote and made an audio recording about a meeting 6th Fleet Rear Admiral Lawrence Geis requested in his cabins: "He told me that since I was the senior Liberty survivor on board he wanted to tell me in confidence what had actually transpired. He told me that upon receipt of our SOS, aircraft were launched to come to our assistance and then Washington was notified. He said that the Secretary of Defense (Robert McNamara) had ordered that the aircraft be returned to the carrier which was done. RADM Geis then said that he speculated that Washington may have suspected that the aircraft carried nuclear weapons so he put together another flight of conventional aircraft that had no capability of carrying nuclear weapons. These he launched to assist us and again notified Washington of his actions. Again McNamara ordered the aircraft recalled. He requested confirmation of the order being unable to believe that Washington would let us sink. This time President Johnson ordered the recall with the comment that he did not care if every man drowned and the ship sank, but that he would not embarrass his allies. This is, to the best of my ability, what I recall transpiring 30 years ago." "

"USS Liberty incident : Details in dispute" : http://en.wikipedia.org/wiki/USS_Liberty_incident#Details_in_dispute