Question:

In what way was the surprise in the attack on the World trade Center similar to the surprise in the attack on Pearl Harbor?

Answer:

Both attacks involved technological surprise: the use of aircraft in unexpected ways for which a defense had not been prepared.

In the case of Pearl Harbor, the US had not realized that torpedoes could be launched from airplanes into shallow water. Up until then, the torpedoes were used in deep water, so their motors could start before they hit the ocean floor. So it was assumed the safest place for the US battleships would be in the shallow waters of Pearl Harbor. But Japanese pilots had been secretly trained to skim their torpedoes in shallow water, and that surprise left the US fleet vulnerable to being sunk from afar by carrier-launched planes.

In the case of the world trade center, the US had not appreciated that suicidists could convert an airliner into a piloted missile. With a three-quarter fuel tank, and moving at 400 miles per hour, it would impart nearly as much energy as a one kiloton battlefield nuclear weapon. To guide the missile, the suicidist pilot required little more than a mail-order global positioning device. Not conceiving that planes could be converted to missiles, no defenses, such as sealed cockpit door, had been prepared.