What frightened the USS Donald Cook so much in the Black Sea?

http://www.youtube.com/watch?v=HkMss5WfF7M
On 10 April 2014, the USS Donald Cook entered the waters of the Black Sea and on 12 April a Russian Su-24 tactical bomber flew over the vessel triggering an incident that, according to several media reports, completely demoralized its crew, so much so that the Pentagon issued a protest [1].
The USS Donald Cook (DDG-75) is a 4th generation guided missile destroyer whose key weapons are Tomahawk cruise missiles with a range of up to 2,500 kilometers, and capable of carrying nuclear explosives. This ship carries 56 Tomahawk missiles in standard mode, and 96 missiles in attack mode.
The US destroyer is equipped with the most recent Aegis Combat System. It is an integrated naval weapons systems which can link together the missile defense systems of all vessels embedded within the same network, so as to ensure the detection, tracking and destruction of hundreds of targets at the same time. In addition, the USS Donald Cook is equipped with 4 large radars, whose power is comparable to that of several stations. For protection, it carries more than fifty anti-aircraft missiles of various types.
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