Tactical Nuclear Weapons
From a practical standpoint, the advantage of a small nuclear bomb is that it can pack so much explosive force into such a small space. (See
How Nuclear Bombs Work for details.) The B61-11 can carry a nuclear charge with anywhere between a 1-kiloton (1,000 tons of TNT) and a 300-kiloton yield. For comparison, the bomb used on Hiroshima had a yield of approximately 15 kilotons. The shock wave from such an intense underground explosion would cause damage deep in the earth and would presumably destroy even the most well-fortified bunker.
HowStuffWorks "Tactical Nuclear Weapons"
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Another reason is the smell of gas in the air reported after the strike, people claiming it was like an earthquake,
lightening in the cloud a few moments after the huge blast and the fact that the said target was a research facility which more than likely would have underground fortified bunkers.
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Striking evidence of the use of American EPW (Earth Penetrating Weapons) nuclear weapons in Syria has come to light. Experts say the proof is irrefutable.
Submitted for analysis, the footage was compared with tests of the 37,000-pound MOB (Massive Ordnance Penetrator), designed by Boeing to be used against Iran’s underground facilities. There was no similarity whatsoever noted between the Syrian “event” and a conventional “bunker buster” including the GBU 57, the largest conventional weapon every to be used.
More Proof
Colonel James Hanke, former Defense Attaché and Liaison between the Pentagon and Netanyahu’s government , reviewed the footage.
He indicated that the GBU 57 is considered too high a risk for use because of its danger to the earth’s crust.
The Syrian/African fault line spreads into Israel. Were it to be subjected to this kind of explosive power, the threat of an earthquake doing significant damage in Israel is a reality. The nuclear bunker busters have far less penetrating power and, I am not saying that this was a nuclear device, not until more evidence is in, but the ‘event profile’ shows striking similarities.
The other problem with the GBU 57 is delivery. Only two aircraft are capable of delivering this weapon, the B-52 and B-2 Stealth Bomber. Israel does not have these aircraft.
PressTV - Was Syria 'nuked'?