The difference was, US military jets carrying nuclear bombs were sent en route in 1967, and were only recalled after the culprit was accurately identified.
Compare Israel’s reckless actions in 1973, also in a war against Egypt, causing the Nixon administration to issue a DEFCON III nuclear alert.
Propaganda> If Israel had premeditated the attack rather than responding to an ad hoc perceived threat, it would have used munitions suitable for sinking a ship (iron bombs, not napalm) and it could have attacked the vessel under cover of darkness.
Israel of course had no right to attack the ship without first ordering it to heave to, but it’s unlikely the original intention was to sink it. This calculus surely shifted considering the extended air attack with missiles, high-calibre aircraft cannon, heavy metallic bombs and burning napalm, followed by a torpedo attack (causing a massive explosion) and sustained machine gun fire on the crippled vessel from attack boats, resulting in a casualty count of 80% of those on board. The miracle is that the ship (barely) limped around long enough to be scrapped upon arrival home. Incidentally, by the time the Israeli speedboats arrived in attack formation, the crew were already using a flashlight to signal their name and position. But it didn’t matter. The attackers machine-gunned the survivors at close range after stopping near the vessel’s fantail, where the Liberty’s name and hull number appeared in large letters (a new oversized American flag had been unfurled). The last thing the IDF did was to machine gun all the life rafts they hadn’t confiscated, even as the survivors were attempting to escape – a serious war crime under international law. They then left the area for a full hour before returning to offer assistance.
Propaganda> More than a dozen investigations have concluded that the incident was the result of a tragic series of mistakes - today used as a case study by the US Naval Academy.
The same US establishment that awarded the ship's Capt. McGonagle his Medal of Honor not at the White House as per the normal custom but at a naval yard so as not to draw attention?
Of course he makes another false claim. Five of the investigations he cites (lifting largely from the 'Jewish Virtual Library') came to no general conclusion, with a sixth exonerating Israel of deliberate intent but scolding it for “inexcusable failures” and “gross negligence”.
The US Naval Board of Inquiry, the one that mattered, was a joke. High-ranking figures had no doubts its report was a whitewash. Senior NSA official Walter Deeley even felt the need to conduct his own internal investigation of the incident, concluding "There is no way that they didn't know that the Liberty was American", while a top secret NSA review concluded the same, charging that the Israeli pilots committed perjury in claiming under oath that they hadn’t seen the US flag. An additional investigation chaired by Admiral Thomas H. Moorer, former Chairman of the Joint Chiefs of Staff, likewise found Israel guilty of a deliberate attack.
None of this would be news of course to anyone who’s read the standard literature on the subject, which is scathing. A good place to start is Anthony Pearson’s “Conspiracy of Silence”  and James Ennes’ “Assault on the Liberty” . For the uncontroversial facts, widely known and admitted in Israel, see Yoram Peri’s “Between Battles and Ballots” . And if anyone doesn’t believe high-ranking officials had no doubts, just ask all the most relevant and well-informed people surrounding the incident:
Dean Rusk [Secretary of State at the time]
George Ball [Under Secretary of State at the time]
Richard Helms, [CIA Director at the time – recall the Liberty was a spy ship]
Paul C. Warnke [Under Secretary of the Navy at the time]
Lieutenant General Marshall S. Carter [Director of the NSA at the time];
Dr. Louis Tordella, [Deputy Director of NSA at the time];
Major General John Morrison [NSA Deputy Director of Operations at the time];
Walter Deeley [the senior NSA official who conducted the internal NSA investigation]
All of the above believed Israel’s attack to be deliberate.
Propaganda> Every piece of information declassified in recent years (e.g. NSA transcripts of intercepted communications of Israeli pilots) supports this.
False, and the most relevant transcripts remain classified (that is, when the US is not pretending they don’t exist).Chicago Tribune: Transcripts of IAF communications show pilots who attacked Liberty in Six-Day War saw a U.S. flag.http://www.haaretz.com/news/israeli-communications-said-to-prove-iaf-knew-liberty-was-u-s-ship-1.230486
|| The report stated that the U.S. National Security Agency - to which the intelligence gathering ship belonged - was able to intercept IAF communications according to which, at some stage, the pilots identified the ship as American but were nonetheless instructed to push ahead with the attack.
If the pilots realized the ship was American only after initially firing on it, as some have maintained, then why did the IDF continue attacking the ship for over an hour? Why has no recording of the shocking discovery back to headquarters ever been released?
Propaganda> None of which prevents people, often feigning concern for US sailors, from muckracking [sic] this incident - nearly 50 years later - to demonize Israel. Sadly, these muckers usually support more recent attacks against the USS Stark and the USS Cole and are indifferent regarding the contemporary attack on the USS El Pueblo (the Liberty's sister ship, which suffered from some of the same problems/mistakes).
Readers might recall that Saddam Hussein was afforded a similar dispensation, as particularly valued allies are, after the vicious attack on the Stark, an “incident” with striking similarities to the Liberty attack – a client state murders about 35 of its master’s seamen during a Middle East war it started through deliberate aggression, claims a ludicrous “tragedy of errors” in mitigation, and is then reprimanded by the master (but with a wink).
Actually, the only peacetime naval incident that came close to the attack on the Liberty before that was the Japanese attack on the Panay in 1937, in which 3 were killed. Richard K. Smith compared the “strangely callous” Israeli response to the far more forthcoming Japanese reaction. Note that Japan couldn’t rely on the US intelligentsia to cover up the attack - a privilege Israel correctly took for granted.
To conclude, I think Admiral Moorer’s remarks say it best:
“These sailors and Marines were entitled to our best defense. We gave them no defense. Did our government put Israel’s interests ahead of our own? If so, why? Does our government continue to subordinate American interests to Israeli interests? … The American people deserve to know the truth about this attack … It is a duty we owe not only to the brave men of the USS Liberty, but to every man and woman who is asked to wear the uniform of the United States."