Most of the threat scenarios portrayed by high-level US officials involved putative attacks with nuclear, chemical or biological weapons, missiles, and cyber-attack.
Little or no attention has been paid to what, with hindsight, seems the obvious ploy of simply crashing a hijacked aircraft into a building. Debate now is sure to focus on what, if anything, can be done to stem such attacks, which are likely to spawn copy-cat efforts around the globe.

One attraction to the terrorist of this type of attack is that it literally makes a bang. Speaking before the attacks, David Claridge, a terrorism specialist with Rubicon International Services Limited, a security consultancy in London says: “Terrorists like to make a big splash. It conveys their political message.”